340 crank in 318?

I'm redoing the entire engine. It's getting all forged internals (I misspoke on my first post). Forged pistons, rods, crank, performance cam. I will be running boost ofc, but I think I'm only going to be running like 13-15lbs, which should be completely safe with all the forged things. Am I over my head? Probably, this is my first build, but where else can I start? I got a spare 318 for $50. I'm confident, it's not my first time doing engine work.

Balancing shouldn't cost that much, should it? Since the 340 was made for the heavy slugs, they would have to drill the crank for it to compensate for the pistons, etc. Or, would they have to add mallory to all the pistons, etc. (not sure which way it goes, never had a balance job done)