[69hugger]

I just did the same swap ("Regular" T-56 out... Magnum F-Body in).
In my case, I also went from the LT pull-style clutch (with external slave cylinder) to a twin disc DYAD and hydraulic TO bearing. The clutch swap required a deeper bell housing which pushed the trans back about 1.5". This also moved my trans mount and shifter location back the same 1.5". But the trans locations for the mount and shifter were the same between the old T-56 and the Magnum F.
My tunnel was modified and has plenty of room for either, but FWIW the clearances seem similar on both tranny's.
I also needed a new driveshaft, both because of the beefier output shaft of the Magnum, and that pesky 1.5" deeper bell housing. I had been running a steel driveshaft on the T-56, now went to an aluminum shaft.
If you're not changing bell housings, the swap should be a straight bolt-in.