Ok folks I have searched the site and am still confused. I know where there is a 70 Elco that needs alot of parts however the price is very right. I also recently found a 72 Grand Prix. The interchangability of parts between these two has me very confused! Elco has no suspension, not sure of frames condition, and very little interior. Grand Prix is supposed to be a roller with a 400 in it. What will interchange, dash, axle, arms, front parts? I can get into these for cheap and the Elco is like a personal holy grail but I don't wann go 2 steps back 2 get 1 forward! Not afraid of work or cutting grinding and fitting!
THANKS if you can help.....

GM A-body front suspension for both cars. If the front on the GP has disc then that's a score. You will need everything disc related (spindels, calipers <-core, caliper brackets, rotors<-useable?, master, valving, hose brackets on the frame, etc).

I'm going to guess the 400 is Pontiac. Don't know much about them....

Frames are different.

Rear end on the GP is probably a Buick-Olds-Pontiac which internally is different than a Chevy rear. After markets parts selection is limited, but it will BOLT UP to the Elky. Check to see if it is a Chevy or BOP if it matters. There are guides online which can help spot them externally. I think the Chevy cover has the "eyebrow" where the BOP's do not. Don't just go by 10 or 12 bolts either. A BOP can have 12 bolts on the cover, but only 10 bolts holding the ring gear to the carrier, hence 10 bolt rear end. You have to pop the cover and count.

Interior, seats are useable (the GP may have an arm rest where the Elky did not), not sure about door componets. Dash? Tilt column is a good score if the GP has it. A/C parts, if there could be salvaged.

Check the Elky for frame rot or major rust behind the seats in the floor area. the GP could be the builder though as metal work is the most labor intensive part of the job second to paint.

All this is based on the GP and Buicks I have parted looking for parts for my Chevelle.