WARNING: Impala lovers with heart conditions should not look at the attached photos! 
We just finished installing a Tremec TKO 600 5speed transmision in the 62. http://5speedtransmissions.com/tr-3550.html The good news is this thing works absolutely terrific.
bang The bad part is you've got to cut out a pretty big chunk of the floor pan hump in order to make it fit. 
It's not really all that bad though because the pan looks stock when it's done. The Tremec's a couple of inches longer than the Muncie/T-10 and it's about the same width, no problem there. But it's also higher and bulkier on top so it hits the transmission hump. You've got to cut out the part that hits, shaping it with a big hammer won't do. I cut out a big chunk of floor and made a new pannel to replace it. I saved the piece I cut out so that I could weld it back in if I ever decide to do a proper restoration. I used pop rivets to install the new pannel because I didn't want to burn all the paint off by welding. I'll post some step by step photos.
1 Tremec beside Super T-10
2 Stock floorboards
3 Shifter hump removed
4 large section of floor removed, Tremec is in place.
5 Cardboard template
We just finished installing a Tremec TKO 600 5speed transmision in the 62. http://5speedtransmissions.com/tr-3550.html The good news is this thing works absolutely terrific.
bang The bad part is you've got to cut out a pretty big chunk of the floor pan hump in order to make it fit. It's not really all that bad though because the pan looks stock when it's done. The Tremec's a couple of inches longer than the Muncie/T-10 and it's about the same width, no problem there. But it's also higher and bulkier on top so it hits the transmission hump. You've got to cut out the part that hits, shaping it with a big hammer won't do. I cut out a big chunk of floor and made a new pannel to replace it. I saved the piece I cut out so that I could weld it back in if I ever decide to do a proper restoration. I used pop rivets to install the new pannel because I didn't want to burn all the paint off by welding. I'll post some step by step photos.1 Tremec beside Super T-10
2 Stock floorboards
3 Shifter hump removed
4 large section of floor removed, Tremec is in place.
5 Cardboard template
I dumped the Powerglides and put overdrive automatics in my last two cars and thought it was the best move I ever made.
We used air powered metal snips to cut out the new patch pannel. We are lucky enough to have a metal roller and shear. We used that to roll smoth bends into the new pannel. The re-usable Cleko pins that we used to hold everything in place untill we installed the pop rivets worked great. I had never used them before. We got them at a speed shop that stock car racers go to. The stock car guys use them alot.
My guess is that the car might be a tiny bit quicker but I think someone with a stock 348 or 409 would see the biggest improvement, especially if they had high gears in the rear end and a transmission with a high first gear like the 2.20 in the close ratio T-10s and Muncies.
