Those studs'll come out of the old pump (in theory). I'd guess they're rusted in beyond anything that your human mind can fathom though. Go to the store and get some shit called PB Blast. It comes in this crazy looking 50's-style marketing spray can, but it really does bust loose about anything. It's only like $3 too.

Silicone sealer in place of bolts is a great idea. That's how I put the heads on my 350. Only pussies use bolts!