Here is what you do to sort the timing.

First and foremost....unhook the vac advance completely and plug its port on the carb so that you dont have a vacuum leak.

Get a timing light and check initial timing at idle. For any performance engine, at least 10 degrees timing should be there at idle. Higher is not out of the question. Give the motor what it wants. Go up in 2 degree increments at a time just to see how she responds.

Then...I always put the absolute lightest advance springs in as possible and check total timing(that way your not under the hood with the engine spinning 4000 rpm or something....the quicker the timing comes in, the safer it "feels" checking total).

Anywhere from 34-40 degrees total is common depending on various factors. I always first find an initial value that it likes.

See where it idles best, and where it starts easiest and quickest(check after warmed up also to make sure it wont kick back on you or roll over or anytihng).

Then...find total timing. Start at 34 and go up 2 degrees at a time with some full throttle runs. Wherever it feels best, make note.

Say for example it likes 14 initial best, and 38 total best. With that in mind, you need 24 degrees of mechanical advance. This is where it gets fun, and recurving comes into play to adjust advance to 24 degrees mechanical so that you can have that 14/38. If you dont wanna play with it, compromise as best as possible.

Say your distributor only has 20 degrees as is. Set initial at 16 and you'll have 36 total. decent compromise.

Hook the vac advance back up to full manifold. If it adds too much adance and you experience pinging at part throttle...tweak the vac advance to limit how much advance it adds. Real real simple to add a stop plate to a non adjustable vac advance to limit how much timing it adds.

Some simple stuff.....check for full throttle! Dont assume your linkage is spot on. If your only opening the butterflies 80%....that would explain a loss in upper rpm power.

Then we get into carb tuning. The list goes on and on