Pulling the motor apart for gaskets and rattle can rebuild. I have read both 292 Ford and 258 AMC to convert to 2 piece seal. So which works better?
Also felpro shows bs13879 and bs40612 for AMC. I just looked up a Mid 70'S car and both those numbers come up.

 

The Fel-Pro # I use is B/S 6141 which is the Ford 292 seal, have used it half a dozen times, no issues.