I'd definately use the plastigauge. Sure it'll take a little longer, but it's better to find a problem with clearances now than later. Did you mic the block and crank after getting it back from the macine shop? Even the best make mistakes sometimes. They're only human. My motto is - trust but verify. Did you also have the shop balance the new pistons with the old rods and crank? Best way to measure piston clearances is to measure your cylinder diameter in 3 spots and compare that to your piston diameter. Hey, why not - make sure all the pistons are 90 mm. Have fun!