Well, truthfully, if a piston fits the bore, has the pin size you need for the rods you're using, and doesnt pop out of the deck far enough to hurt the top ring, it "fits". I wouldnt run it any further up then down about .040" from the top edge to keep it clear of the chamfer of the bores. You can use a low compression stock piston in some big block builds to get a "0" or close to "0" deck height with a longer stroke crank. I dont think any 360 pistons or low compression 340 pistons will work in a 340 block with a 3.58" (360) or 4" stroke. You can take a factory crank, and offset grind it undersize and increase the stroke as much as .060 if the crank is good to start with. The thing is, you are left with a piston with no valve reliefs, that's heavy, and that isnt very strong, and, the max you can get is only 10" more. Not really worth the cost, as offset grinding will cost more than std crank work.