Anythng you do that changes the original castings more than 1" in on the intake/exhaust port is illegal.

I've soaked mine in solvent and then brushed them to get carbon out/off. Bead blast is probably ok if you go easy.

On the flow testing, why do it at home? We maybe lucky I guess with a local engine builder with a flow bench, but I think he charged me like $25 to flow test the carb manifold versus the FI one.