Question: who offers a 6.2 rod and forged piston for the 250?
Most all connecting rod companies offer them as a custom part, but also at a custom price. 5.700" and 6.00" are the norm for the 250 engines for off the shelf, modest pricing rods.
As for piston sizes, you will rarely find a 250 or 292 that will clean up at .030" over, and i've seen many that had a couple of cylinders that wouldn't even clean up at .060". The front 2 cylinders are the worst ones typically. So find a block and get it rough bored first to verify it will clean up at an acceptable bore size before buying pistons.
You seemed surprised at the cost of pistons, many people expect that building a 6 cylinder is somewhat cheaper than a V8 because there are 2 less cylinders. Its often considerably more and even with less HP than you'd get with a V8 unfortunately. So don't let cost hinder you.
