Do your homework. Figure out what HCI it is that you want to go with.
Once you've settled on one, give the vendor a call and ask them what rotating assembly will work best for you (pistons, rods, crank, etc.). Settle on and purchase the rotating assembly that you want and take it to your builder along with a set of gaskets, seals, and freeze plugs.
Now the only thing you're paying the builder for is labor. So long as he does his job correctly, you'll have a complete combo with matching parts that all work well together. The right pistons, to match the valve/head/cam combo that you will be using. No muss no fuss.
You might even save some dough.
I'd be leery about just slapping an HCI or even a blower with some budget rebuild from Bob's garage. At least if you pick the parts, you know what will be in the thing.