it is a big block chev, not sb.
I remember from when I had the heads off that it was lined up properly, but I suppose it could have slipped since then.
I'm not really able to look at the keyway unless I disassemble the front end, I'll just use a piston stop.

But is popping something that retarded timing does?

When I rotated the dist to adv it while it was running it would really smooth out and run great (this was around 35 according to the balancer). Backing it off closer to 20 would make it kind of choppy and a clearly different exhaust note.