454 1983 truck

I'm ready to send my block in for boring and cleaning.My question is should i get the pistons first, it will be a 20 over bore job,and i plan on using some type of cast piston.My harley bore job required the pistons to be there for the job. what do you guys do

Pretty wise to get the pistons first. Machining can match to specs with out guesswork. They'll have the numbers they need to do a proper job.