Whoa!,
If in fact, the entire length of the transfer slot is exposed under the throttles, at 26* advance, then I have three questions;
1) Are you sure your balancer is indexed correctly to TDC, and
2) are you sure the cam is degree'd correctly?
3) lol, are you sure your timing light is working correctly?
I am assuming you know what the transfer slots look like.
Cuz if this is all correct, then your engine is asking for a heckuvalot of air. And IMO you might need a hi-altitude calibrated carb to start with.