If your machinist is a friend of the family-----------------------

You can take off or short out the wire to the plug on that questionable cylinder and if its a piston slap it will probably quiet down--------

Full floating pins?????? how much clearance on them????/seems to me like you have a mixture of things that aren't the best choices for compatibilty----forged pistons but cast crank??

How did the machinist do the bores?????boring bar with a block fixture??? or just clamped to the block deck????how was the bores honed???electric drill and bottle brush or a CK10 type hone with deck plates torqued down?????I'm not trying to be an ass hole , but there are lots of shops that don't have proper equipment to do a top level job and they take short cuts and talk a good line of bs