Howdy back Brian:
I can say from experience that .070" is doable. That's what I did to mine. Probably not a good idea. What is your engines deck height? Mine was .150". At some point structural integrity becomes and issue.
If I were to do another 250, I start by using the 255 V8 pistons which are .085" taller than 200/250 pistons. But you said you had a set of forged stock 250 pistons you intend to use. You could also consider offset grinding the crank to raise the pistons up another .010" to .12". Also check out the Tempo rods recently discussed here.
PS- hold off on head work until you have figured out dimensions or your CR will be through the roof.
Keep us posted.
Adios, David