The front crossmember from my '77 Scottsdale fits my '66 with one exception. The '66 was missing a hole in the frame for one of the fasteners on both sides. A drill bit fixed that. Otherwise, it was not as hard as getting the crossmember out of the '77.
When you get ready to pull the crossmember, pull the motor too. I tried not to and ended up doing it anyhow to get the nut buster on a frozen fastener. Leave the wheels on, too. It makes it easier to move around and they aren't in any way if the motors out.
You can pick up a front crossmember out of a "parts-yard" (I don't buy junk) for about $150. I just happen to get a whole running truck for $200. Got a nice truck 350/4-bolt with forged crank (wide parting line), a good TH350, tilt column, power steering, a good seat, a gas tank and more, to boot. Buying a donor and stripping it is work, but it pays well. Worth considering.
I wouldn't recommend the rear swap to leaf springs. It's more work than it's worth unless the parts a free, and you'll give up ride quality. The trailing arm set-up is the thing to have IMHO.
Good Luck on yours
