[1950Mercury]

I am in the near future thinking of building a 421 or 428 engine. Since none are falling on my lap at a decent price I have been considering a 389 block or a 400 block. I already have a 68 0071 400 block which is 2 bolt main. So the question being how are these aftermarket cranks with 3" mains working out in 2 bolt main blocks? is it basically get correct pistons for the 4" stroke or is there a bunch of machine work on the crank? in other words are these cranks any good? I was considering a cast crank but what I see from Butler it takes Chevy rods. Is there a 4" stroke 3" main that uses the 6.625 Pontiac rod? I am not after huge cubic inch or super high horse. Probably 425-450 tops. I would like to find a 8789 block bore .030 and be happy with a 428. Otherwise I will take this 0071 block to +.060