When my 426 was dynoed, the best pulls were at 28. I also have heard and have experienced with other gen 3 builds, that they do no require " normal" timing. Usually around the 25 or less. Obviously, real world and dyno conditions vary.
Is your 426 a gen 3 or a gen 2?
Going to make 1st pass at 30 for reference, then try 28 and see what happens. Then 26.
Thinking about finding a chassis dyno in the area. Problem is most of them aren't familiar with Mopar, just late model Ford, Chevy and ricers.