[ERA Chas]

I think your cam is too big for your heads and carb. The shrouding issue is very important. If you mean your LSA is 108deg, you're bleeding too much cylinder pressure. 13.5 on race gas allows much more spark lead, sooner.
My 427 made 467WHP on open headers, 462 on your SS sidepipes. It has 1308 cfm induction, Shelby Stage II's with 2.25" intakes and a .613/.633-244/255 with 110 LSA Ultradyne. Spark is 38-40 deg (same power) all in by 2600. Compression is 10.33.
Your stalling problem is improved by installing vent whistles on the metering blocks and cured by sealing an air pan to the hood scoop.
Good luck,