you may to find a good trans guy to get the OD unit to handle much boost better plan a HUGE trans oil cooler to handle the heat if you are going to run a converter at all
I have a used stock LR4 in the 'maro, awaiting a used stock 4L80E, while I'm building my 1200-HP LR4 which will get a Jake's Performance 4L80E stage 5. I used a stock 700R-4 from an '88 'maro for stock transmission location, to adjust the LSx mounting. The 700R-4 is out and gone.
I considered a Tranzilla T56 from Rockland Standard Gear, but their best one is a lame 2.29:1 first with a stout 0.76:1 sixth, so the ratios are far too close. Besides, it's only rated to 1200 HP and 1000 TQ, which leaves nothing for improving the engine, while Jake's stage 5 is good past 1400.
I'm sure it will take a couple of tries to get a custom torque converter matched to this application just right, but I accepted that as part of the price of big power. In the world of GM V8s, transmissions have always been the biggest expense, even if starting with a TH400.
There used to be 2.14 gears for the GM passenger-car-use 12-bolt 8.875" axle, and if I could get a set then I'd just use a SM465 and modify the floorpan tunnel to match. Or if I could score a GearVendors and a proper 9" Ford, but even with Quick Performance offering the bolt-in housing with 35-spline shafts for under a grand, it's still less unnecessary spending to invest in swapping a salvage yard axle.
For dragstrip use the obvious winner is a F150 / sterling 9.75" since there are millions of them for under $ 200, and they have 3.08:1, 34-spline, and disc brakes. Just gotta do custom wheels or redrill the axles and rotors, then address the mounting brackets. It's not noticeably wider than the '93-'02 7.625" axle. And if I could score a GearVendors, I would never even consider any other rear for a multi-purpose 1200-horse car.
You guys indicate a Ford 8.8" would be adequate on salt, so I've researched which vehicles were closest in housing width. I can have it 2.73:1 and 31-spline and disc brakes and Traction-Lock for under $ 200, by being clever at the salvage yard.
So I'm still wanting a hardtop '85 TransAm, more than a record run. The D/MMP is so tempting, I may end up with more than 1 vehicle for the salt. Each starting point can be had for under $ 1000, and use the one engine for several vehicles.