Well I seem to have fixed the issue. It ran a lot better after I pulled everything off and reinstalled the timing chain, but was still backfiring under hard acceleration.

I made the mistake of setting the initial timing with the vacuum advance hooked up. I realized this and as soon as I unhooked it, my timing dropped from 15 to 5 initial... I reset the timing to 15 and took it for a ride (with the vacuum advance still unhooked and capped off) and it ran great. I still haven't hooked it back up yet.

Thanks all for the help in what to look for! As always, it is appreciated. - Brian