I was under the impression the OP was talking 1970 E-body since he was initially referring to the so 2983696 (pn 3420884 ) being a roadlamp relay.
I cant comment on the B body models but I believe the 2983696 was used in A body as well .

If I can find that old thread, it goes into deep detail on all relays, buzzers, harness, 70 and 71 all being different.