Do these trannies from f-bodies interchange? I've never seen a 700r4 behind a 2.8 to see if they interchange. What other types of cars or trucks to these trannies fit in? Thx. in advance.

If you are talking about swapping a 2.8/3.1L 700R4 into a V-8 F-Body, then no they are not interchangeable. The bellhousing on the F-Body V-6 700 is different from the V-8's. The 700R4's used in Astro/Safari Minivans and S10/S15 SUV's and P/U's with 4.3 V-6 and 2wd can be used. I wouldn't recommend using the 4.3L 700 though, because it has a lower torque rating than the V-8 700R4. If you can't find another F-Body specific 700R4, you can substitute it with a 700 from a B-Body(Caprice),1/2 ton Cheyenne/Silverado 2wd V-8 P/U or V-8 G10 Van. Some G-Bodies(Monte Carlo) came with the 700 also. The G-Body 700R4 will work also. I had a 700R4 from an 86' Silverado in my T/A before I got my 4L60. Vette 700's won't work because they have a shorter output shaft than the F-Body 700 does. 4x4 700's won't work as well. The others mentioned will interchange with no problem. Just remember to swap your F-Body tailshaft,governor, and speedo gears to the new/used tranny.

I knew about v6 and v8s not being interchangeable. Can you take a 700r4 that was behind a 3.1 and put it behind a 2.8 and visa versa from a 3rd gen f-body?

Yes, they're both 60* blocks. Essentially the same engine, as far as this is concerned.

X2 about swapping 3.1L 700 into a 2.8L F-Body. I'm sorry I misunderstood your original question. You could also use 700R4's from 2.8L 2wd S10/S15 P/U and Blazer/Jimmy.