426 engine blocks are fairly rare and anyone who can afford a block could easily afford custom pistons. 413 blocks on the other hand are fairly cheap to find since they aren't very desirable. Therefore, I bet you could sell some inexpensive pistons to low buck guys who round up a 413 block and want a decent compression piston. If it was me I'd design a 413 piston that provide 9.5 to 10.0 compression with a cheap head like the 440Source or the E Street. If you do that you might find a market niche in the low buck area. I don't think I'd bother making a 426W piston. Demand for them has to be close to zero.
