440 Crank in a 383

383 block stronger...is that true? What makes them stronger?

I agree that the finished crank cost is probably comparable, but if you are only buying pistons and having the crank turned them the 436/541 is probably still going to be a bit less expensive.
Go to 440 source, see "everything you wanted to know about blocks, and more".
Edit: any block can have good or bad cylinder walls, depending on core shift. Always a good idea to get it sonic checked before putting any money in one. Rumor is (contrary to what even Ma Mopar said) there are no thin wall blocks.