The W72 platform is more than capable of going from 220 hp to 440-500 hp, even without a stroker kit- the stock iron 6x-4s can be ported to 250+ cfm, surface milled to reduce chamber size and increase SCR, better pistons and rods added to support the increased output. The cost of this is similar to building a 400/461 stroker, but the end result appears to look the same as a stock W72 and the element of surprise is excellent.
I used to think these engines were hard to find, but in the last year or so I've bought two of them, so they are out there if you look hard enough. One of them is a runner, and that is going into my 76 TA- I cannot bear the thought of using any 500557 400, so a W72 is the perfect substitute IMO. The other shortblock is patiently waiting for a home- that one may get the "stealth stroker" treatment- I want to see how stock 6x-4's work with a stroker.crank.
Geno