Budget racers quickest stock piston and head motors

Sounds like you are not a total rookie.

I'd say the cam not being degreed is a big one since you could be leaving some power on the table. That would also change your tuning parameters right from the start. It's likely close but if you decide to delve into it and see where it's at, you might find it responds differently.

I would also try to bump up the initial some. How quick does the timing come in? You will probably need to limit the mechanical some though so it's a balancing act.

Open headers should help, at least it's not breathing through manifolds! But, lack of back pressure may be an issue with the stock intake and small carb, i.e., reversion with too much air. Carb might be too small for WOT. Can you try a larger carb to see if it helps?

Small blocks need gears for sure. 4.10 gear should be OK but you are correct in that the tire might be too tall. Where do you shift it at? I'm guessing under 6,000 rpm.