I have an early 4L80e in my 68 Camaro and it's a tight fit. The cooling lines are more forward on the early cases and have more clearance.Beth, I'm not yet done with this TH400 build. Those photos are just the beginning stages. I still have to assemble the rear gear train, modify the pump, ( although a minor modification) and install everything into the new case which also includes the intermediate clutches, and the center support. So I'm not done with this project just yet. These are really baby steps cuz I'm still a novice at this trans building thang. Anyway, as you likely already know, it's often said that a 4L80 is like a TH400 with an O\D gear added. I'm not sure, but I think the 4L80 case is slightly bigger than that of the TH400, ( which BTW might very well be due to the O\D gear). I already have a TH400 in the car now, ( which is only rated for about 125 HP less than what I expect the engine to make) and it was such a tight fit for me to install that TH400 into the car, that I had to literally take a 20 lb sledge hammer to "massage" the floor tunnel to get the trans to fit while the car was on my brother's lift, ( another reason why I went with a Reid SFI approved case, since I won't need a trans shield, and there's no way I can fit a trans shield in the car).
So my guess is that I'd have to cut the entire floor tunnel out of the car, and get a buddy of mine who does body work, to fab up a whole new, bigger floor tunnel for me in order to fit a 4L80 housing case. That's something I'm not willing to do merely to have an O\D gear. Another thing is that I've had two transmissions in the past in other cars with less power, ( 475HP and 530 HP) with overdrive gears, and I blew the O\D gears in both those transmissions from merely street driving, (the last one I blew the O\D in on the highway late at night at 140 mph). So I'm not a huge fan of O\D gears. I guess I'm just too rough on my cars and on transmissions to have one.
Good luck with this build !