Piston down .255" won't work - even a blown motor needs quench (unless you use methanol).
Very few commercial rods in 7.25" × 2.10" journal - most of the long rods are for either 2.20" (BBC) or 2.375" (BBM). What you save in piston cost you spend in rods. I can't find a 2.10" rod at all - everything is either bigger ($$$ crank work), or smaller and shorter (1955-67 SBC), or smaller, longer and weaker (Dodge 230).
I would guess that any cam you would use would have less than .255" lift on overlap, so valve relief position isn't a problem.
What you really need for low-comp is a "D" cup piston (which any can supply) with an open area under the valves and quench under the closed deck, etc.
You can open the chamber to get some volume, the obvious is relieving the wall around both valve OD - but don't move the quench line opposite the plug.
For such a heavy chassis I wouldn't use such low static CR. Even 8:1 is an improvement - regardless of boost, low CR means any big cam will make very poor low speed power.
More details: cam? fuel system? max boost?
