Technical Flathead Vac Reading

So I got the carb issues sorted out, and finally got the cooling issues taken care of on the flathead ('51)
Also realized the dizzy was a tooth off and got that sorted.
Now I am ready to fine tune the timing.
Currently, the mark is just a bit before the pin on the block. This was the point where it started idling good.
My dizzy is a Mallory dual point, isky max 1 cam and dual 94's on a Edmund's intake. There is a single port in between the carbs on the intake and as far as I can see this is the only point I could possibly pull a vac reading.
So my question is... with this set up, what kind of vac numbers should i expect to see with this set up?
And
If i understand correctly, i should advance the timing untill i get the maximum vac reading and then back off just a bit.
Any other suggestions or steps that need to be taken?
Thanks as always
Chappy