Did the A518-swap on my '73 Dart;
USCartool saying no mods are necessary is a big pile of BS.

- Lower crossmember needs to be modified. Best to use '80s GM mount.
- Upper crossmember needs to be removed and replaced by either curved flatstock or full left to right crossmember welding to floorboards.
- Tunnel needs a few hammerkisses in some places.
- Need longer speedometer cable.
- Larger diameter cooling lines needed.
- A518 tailhousing needs 1 or 2 ribs ground off on the sides.

I didn't gain any mpg in my daily driven A-body but the car did become more fun to drive.
Using 3.55 rear gears.