Look along the side of the engine you will see a place where the gasket sticks outside the head/block in a recess, there will be 1, 2 or 3 holes in it, this shows the thickness so you need a replacement with the same no. of holes in.
Don't think a crank change will matter, I think it is to do with how far up the bores the pistons come which is more likely to be a function of the machining in the block manufacture rather than crank.
If you put the thickest on you would just lose a little bit of compression. Not sure how much difference this would make. The thickest gasket actually has no holes in it, but is an extremely rare thing to find on an engine, most are 2 hole and a few 1s and 3s (on 300s at least - same gasket)