Can't really simplify this one, my friend.
Option One, the cheapest. Find Keith Black or TRW and get them to sell you some 305 Chevy pistons in std size, and take your engine bore to 3.736", a 56 thou overbore. Not everyone is keen to bore out this much.
Option Two.Ross and Wiseco make totally custom pistons, and they will make you a set of six to your requirements. Exact duplicates of the cast pistons critical dimensions, and you could specify +20 thou over (3.700") and then have plenty of meat in the bores.
Option Three:In terms of cost, perhaps its better to get 2.0 Subaru forged pistons, which have very low deck heights, and mix tem with a set of 300 Ford six rods and make them fit a bored out or bushed up con-rod.
Here's some data, posted by Floridaphatman a while back:-
Subaru 2.0L 2001+ 5.135â€rod 2.165â€inch main journal .840â€inch wide at the journal .905â€diameter at the pin 2.953"stroke 3.622" (92mm) 1.287" piston diameter. You'd have to find some +60's to make it work, may be hard to find a stock bore to hone up to 3.682"
There is a link here at
http://members.aol.com/FE3N/rods.html on pistons.
Forged pistons are so jolly expensive, you'll need to rasie a bank loan just to get them. Hope your gonna thrash the beanie of your 250. The are for guys with a seroius penchant for blowing $$$.