Interchangability

Didn't know where to post this, so if it needs to be moved, my apologies. My 75 Dart Sport may have a cracked block, There is a 77 Aspen being sold for 250, this includes 318/727 and the seller claims and 8.75 rear axle. (My Dart has an 8.25 6 leaf already.) The Aspen also has a nice 2.5 inch exhaust system, plus the large brakes.

I know 250 is a good deal, but will the 8.75 axle and the exhaust interchange and are there any body/interior pieces that interchange. -BD