Will 20x10 rims with 295/40 20 tires put in the back of the car fit on a 1970 cutlass?

 

Yes, I have 17x11's w/6" backspace and a 315-35-17 on the rear of my 72 and they fit great. I also have a set of 18x10's w/6" bs and 295 tires and they will fit all my A-body cars. That 295-40-20 would be over 29 inches tall so you might go with a 295-30 or 295-35 or comparable size if you do not want to go with that tall of a tire.

 

It might but as mentioned above a 295 -40 is almost 30" tall. If you have to do 20" and 30 or 35 series will be a better choice. A 18" or 19" wheel will look better IMO though.

 

People can make anything "fit".
The question is, will it look good.