Horsepower guess?

Since that cam is pretty darn close to a stock 340 grind I'd say 275 at the flywheel. Besides the low compression, your limiting factor will be the exhaust and carb (I understand you are using what you have and building in stages). You'll certainly notice a difference with dual exhaust and a 750 CFM carb (the heads and manifold will certainly support it). But the low compression will hurt you.

I would think long and hard about KB107 pistons and a Comp XE274 cam, and a Thunder AVS carb.