early A - later A interchange

ALL front suspension pieces will interchange EXCEPT the K-members and their associated steering linkages. ALL A-body torsion bars interchange. ALL A-body springs interchange. Steering boxes interchange. Rear axles interchange. Driveshafts are wheelbase and axle dependent. Radiators (22") pretty much interchange if you use the matching water pump.

When it comes to body hardware, heaters, speedo and e-brake cables and the like they tend to interchange within year groups. Basically 63-66, 67-72, 73-76. A lot of the more esoteric stuff is pretty much year specific.