I've only had fitment experience with the STSmachining mounts, which put the engine/trans too far back for the shifter turret to fit in the tunnel. I was set on not doing a crossmember notch, so I kinda said "eff it" and got a TKO, which has actually gone fairly smoothly (with a few expectable unforeseen caveats).
Three ways of keeping the T56:
1. Modify the back of the tunnel; probably also the parking brake handle (which is really pretty trivial, swap-wise)
2. Build a weird bastard T56 (maybe the tailhousing from a Mustang Cobra?)
3. Make your own mounts, notch crossmember, go with F-body oil pan. Will probably need to move the radiator forward and/or convert to Corvette or F-body accessory spacing if you were starting with a truck engine.
Side-to-side-wise, T56 should fit if you remove the reverse lockout solenoid (a freeze plug from a 1.8L Miata I had sitting around worked well) and the neutral safety switch (the drain plug from a Subaru was a match).