Put a T56 Magnum behind the 440 in my A-body 1968 Barracuda. We will see how this turns out... just going to put a bunch of pictures and notes and work from there.
I bought a crossmember kit from ToddRon Restorations. ToddRon Restorations
When I bought the kit he had only done this conversion with a small block and the Ford version of the T56 Magnum. My car has a 440 and the folks at American Powertrain insisted I needed the GM version and the subsequent different bellhousing or I would be severely limited on clutch options. I purchased the kit from Ron knowing full well it probably wouldn't fit. I ended up doing some modification to the transmission crossmember to make it work. I fed this information back and the newer kits he sells will work either way. Transmission is a "Tremec Magnum Close Ratio 6-speed for GM" part number TUET11009. Tremec Magnum Close Ratio 6-speed for GM TUET11009 - American Powertrain
Gear ratios are 1st 2.66, 2nd 1.78, 3rd 1.30, 4th 1:1, 5th .80 and 6th .63.
Clutch is their "Atomic Twin" rated for 1100ft-lbs of torque. Clutches - American Powertrain
Here are a few picture showing the floor cut out, the upper piece being welded into place, the tunnel, and the finished floor with console brackets. The shop I had the paint and body done also is used to doing some fabrication work. The shop owner is a friend, we worked together to fit everything and sort it all out.
Here is the flywheel with the pilot bearing installed and here I am checking and adjusting the runout. I am using a dial indicator attached to the crankshaft measuring the runout on the bearing surface for the transmission input. This is making sure the transmission is aligned to the crankshaft. I ended up having to shim the bellhousing to get it square to the engine, then the TIR was good. It has been a while... I don't remember the numbers.
Installing the clutch assembly was simple. There are two discs. First picture is first disc plus the plate that goes between the two. Second picture is both discs. Third and fourth are with the pressure plate.
The hydraulic throw out bearing was a project. I measured the clearance / depth of the throw out bearing and even with all the "washer" type spacers they sent it was going to be too far from the pressure plate. I talked to American Power Train tech support and they determined that I should have been sent a different spacer. They took care of it and we were in business. First picture before correct spacer, second and third are with. Without this spacer my car would not have been driveable!
Here it is mounted to the engine and on its way to being put in the car.
And a few pictures showing the console and shifter:
Update March 21, 2020: Got a revised and improved version crossmember from ToddRon Restorations which has changes to the design based on feedback when I did this work 7 years ago. It puts the transmission tailshaft up about 1/4" higher, so I'm expecting that should help the drivetrain angle.