A (forged) 340 Crank is Not a (forged) 273/318 Crank?

Now I am thinking about aborting the re-assembly of this core 340 I purchased (with new rings and bearings), since the forged crank it came with does not have the holes drilled in the #1 and #4 connecting rod throws. I don't have a clue if the reciprocating parts (stock connecting rods and aftermarket cast pistons) are balanced correctly to this crankshaft. And I don't know anyone in the area who can balance a motor. Just to be safe, I think I will find some Baja 1000 racers and ask them who builds (and hopefully balances) their motors down here.