What are the specs on the cam? If it's not bumpy 15in of vacuum is late ign. timing and it would do what you say it's doing. Whats you total timing at?

A slight vac leak will still let it stay steady(usually just a bit lower of a reading) as there's no intermittent interruption in the intake tract(which would make the vac gauge jump around) only that the mixture air/fuel ratio in the intake tract is now off enough to cause driveability issues. but if it got lean enough to cause a lean misfire then that would cause the gauge to dive for a split second as that cyl didn't do it's job.

Are you still using points? sounds like a bad distributor to me. Do you have the vacuum advance hooked up?? It should be on ported vacuum and not manifold. manifold will make it backfire when letting off as it pulls the timing a way up.

if your carb goes lean it will backfire on you, and since it doesn't pop when you ease into it, I would look there

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

Good for you.
I am glad it wasn't something to painful$.
Just goes to show you we all forget things from time to time. Hook that advance back up and go have some fun.