Distributor advance springs

A '74 distributor and a '77 distributor may have very different advance curves even when using the same cam.
I don't know that for sure, but its very possible because each year the emissions package was tweaked.
See the specs @Bugman posted here for '78:Distributor recurve (scroll down to see them plotted).
Notice one distributor application has the the initial timing of 2* ATDC at 750 rpm while most of the others are at 12* BTDC at 700 rpm. Big difference!
Compare those with 1967 non-emissions distributor in a car which was 5*BTDC at 650 rpm.
Big difference again.
We can check what '74 had but the point is that the initial is specific to the distributor because of differences in the advance curve.
So if you are setting the '77 engine for a 12* at 700 and using a distributor intended for 5* or 2* BTDC at 700 rpm, then it will ping and possibly even damage things at WOT.