Found a factory GM brace in my box-o-braces that fit almost perfectly between the right frame-rail (as it arches down to the right subframe's mid-mount point, just behind where the CV comes out) and the engine's rear alternator support bracket (which is no longer being used). There are several holes in the frame rail there, and the inside is accessible from the side, making it a perfect mounting point. Unfortunately, as I've lowered the engine, the holes no longer line-up so perfectly -I had to drill an extra hole. Ultimately, I will be adding structural plates both inside and outside of the frame rail (bolt-on pieces).
The right-side will be supported by this brace in the rear, the factory Z-34 mounting bracket on the front with a big-block Mopar engine mount between it and the subframe, and the original '95 3100's dogbone brace bracket (which bolts perfectly to the 3.4 DOHC, of course) modified to bolt up directly to the subframe instead of just using a flexible dog-bone torsion-brace.
I started the rough-cut on the radiator tie-bar (upper core) support, using both the GTU's 3800SC swap and the Teal Indy's 4.0 L47 Aurora swap components as models. This will have a brace holding the engine from the front left (original Z-34 torsion brace/lifting eyelet). I will have a hard time making an H-brace framework, like I did in both of the other cars which attach both strut towers together in the rear and brace into the upper tie-bar at the front, due to the height of the throttle-body on the 3.4 DOHC and the future planning of a turbo install, but I think I can attach the ends of the support directly to the strut-towers instead.
Also got most of the transmission's mount done -a slightly modded variation of the one I designed for the '90 Turbo 'Retta that supports the Muncie from underneath and bolts into the left sub-frame.
Finally, the rear of the engine will have a bracket off of the EGR pad on the intake with a small torsion-brace pushing against the strut-tower brace (sourced from a GM H-body, like the GTU and V-8 Indy have), but while fairly stout, that whole thing is cast aluminum, so it will have to be the most flexible of all the mounts.
I like supporting the engines in these cars at several points, suspending them from a 'web' of lighter mounts and braces, rather than using two or three big, bulky mounts to hold the drivetrain in place. Basically, these cars have too much flex in them as it is, and the engines I'm putting into them are physically too big to go slapping around inside the bay. Using several small mounts makes the engine more of a stressed component of the car's structure, like a motorcycle engine, and distributes the stresses into the car more evenly, rather than having a burdensome lump thrown into the middle. So far, the GTU has performed flawlessly in this regard for years and years.
Now I am looking seriously at moving the battery to the passenger-side of the car (again, due to the turbo), and finding that GM stamped this side differently, more like a step up to the strut tower than a ramp, and the original passenger-side engine mount frame obstructs the battery placement.
Considering seriously attacking this piece with a grinder, to avoid having to dump the battery into the trunk...
But I'll wait until I know for sure how the turbo will fit in the bay with the 3.4...