Pthbthbpthba! (That is the sound of me biting my tongue.)
Okay, until I get it back together and back on the road, I really can't say too much. But, as the current owner of the only N* Beretta I've ever seen, I can say a little...
The car is a teal Indy, original 5-speed digital car. When I first saw it, the builder had it put together well enough I thought is was stock at first. I wasn't too into Berettas back then, but it was a decent build-job. Some years later, it has fallen into serious disrepair from lack of use and other issues. I got the car in trade, and it seriously needs some work to be back on the road. Technically, it is not a true N*, because it is the Aurora L47 4.0L, like Weba mentioned (he is my Beretta hero, have I mentioned that yet?), but it is still a 5-speed.
For anyone interested in the facts on this, here is a quick run-down of what you would be facing to implant one of these monsters:
-Custom engine-mounts. Like my 3800-II SC -powered GTU, there isn't much wiggle-room in the bay for the engine, so solid mounts might be the only practical solution, which means vibration. The N*s and the 3800s are smooth engines, so it can be tolerable, but it won't have the comfort of stock. Although I proved that the 3800 can be successfully mounted in a Beretta without modifying the frame of the car or needing a welder, the complexity of the N* setup probably requires at least a little of both -at least a few holes drilled into the car and some custom brackets made. I'm still building better ones for my N* Indy that will actually hold up, though probably not look so stock, and I wouldn't want to attempt that without a welder.
-The engine is too long to fit properly in a Beretta. The crankshaft pulley rides UNDER the frame-rail, so you loose power-steering, unless you can figure a way around that (my idea is to use a Quad-4 power steering pump, which has the tiny driven pulley designed to come off of a slow-turning cam, and build a bracket to run it with the cam-driven water-pump. I would then use a fourth-gen Camaro remote reservoir due to space restrictions. I don't know if this will actually work though, so you might have to loose power steering altogether.) A/C and alternator are fine, but you have to carve a small notch into the vertical frame-bracket that comes down to the outside of the radiator core-support -not a big deal, but it is still a mod you have to do. You also need to cool the alternator with an electric fan (mine has a Fiero distributor/alternator cooling fan, it is a small unit designed to push air through tubes to remote accessories) because the front cooling vane-fan will not fit unless you hack the heck out of the Beretta.
-The stock serpentine belt-tensioner will no longer fit or be useful, so build a new one. If that doesn't scare you away, you don't know what I'm talking about.
-The transmission shifts a little too far to the left, and there is a lip underneath the Beretta that needs to be bent slightly outward if you ever want to replace the clutch again. Also, the entire engine and transmission has to be dropped to separate the two, so maintenance will be more complicated. The alternator is also harder to get to. Custom CVs don't seem to be needed, but there may be a little binding on the left, the builder wasn't sure if they were just bad or not. Custom mounts are probably needed here too, I don't think stock ones work unless modified.
-The N* oil-pan will not clear the Beretta's right-side sub-frame. Mine has a tiny notch cut out of the sub-frame, and a modified oil-pan. My oil-pan is also cracked, which was the main reason the car was parked, and I don't have the facilities to weld aluminum anymore, so I will eventually build a new pan out of steel. Again, run away! Run away!
-The standard Beretta radiator may or may not be enough for the N* -mine has a 3-core copper job that was used in the special turbo Grand Prix, it is narrower and thicker. The radiator cap is conveniently next to the engine's oil-fill cap, too. But try to find one of those radiators new now...
-Expect the standard issues of radiator hoses, heater hoses, and A/C lines (if applicable) -these aren't too bad though. Remember you will also need a custom exhaust system built for the car.
-Wiring... If this intimidates you, at least you know it won't be like plugging in your TV set. This is about the same as the wiring-job I had to do for my 3800, which was time consuming, but otherwise not too bad, but I am comfortable with wiring. Get ahold of complete schematics for both donor and Beretta before contemplating this. Or, just throw money at it and have Megasquirt or some other do the work for you, no one will laugh, I promise!
-If you have an older Beretta with the huge upper tranny-mount post on the left, you will need to cut that down and build a new mount or reverse the intake plenum so the throttle-body and MAF can clear.
...And if you want a manual tranny...
-You will need to build a custom jackshaft (intermediate shaft from the transmission to the right CV joint) support bracket.
-The N*-family mounts the starter on top, between the cylinder banks, so the transmission will need modification.
-N*s did not come from the factory with manual transmissions, so the flywheel is expensive and not many people make them. When my car was built, apparently NO ONE produced N* flywheels for sale, so the original builder made one for the car.
-Shift-cables interfere with the engine, so a new bracket will need to be fabricated.
Congratulations! That is a simple project, isn't it? NO, it isn't. Is it worth while? Only you can answer that for yourself. Personally, I think if you can afford to have your car taken apart for several months, are comfortable with the wiring and the fabrication and the cost, and just really want an oddball V-8 Beretta, then yeah, maybe it is worth it. But it certainly isn't easy, and building a healthy V-6 or Quad-powered Beretta that will crank-out the 240-300 HP that the older members of the N* family is rated at would be faster and maybe cheaper. But to each their own, so pick what you want and pay your fees, just have fun with it or you did it wrong.