At Summit I see the KB356 for $420, the KB190 for $324, so $100. Why would you have to mill the piston? It's made for the stroker and a Magnum head. I didn't do the math because we don't know what his deck height will be and I'm at work but even if there is a problem thicker head gaskets are available. I don't see the block clearancing as a problem. An hour with a die grinder and carbide bur will easily accomplish the task unless you are totally inept at mechanical things, in which case you shouldn't be building an engine anyway.

It just doesn't make sense to not consider the stroker for it's obvious low end grunt capabilities over the 360.

As for the fuel mileage question, gasoline engines deliver their best fuel economy at the RPM where they are most volumetric efficient, which in a stroker would be at a lower RPM. All subject to head flow and camshaft of course. You would have to build a more radical 360 to get the same torque as a stroker which would mean having to turn it harder.