Wheel spin is more associated with torque and low end grunt... that is compression ratio related. And your intended use typically is better met (by most folks) with a wider torque band and lower end RPM performance....compression ratio again. So you were on track to begin with.
What compression readings did you actually get?
One other thing to help low RPM torque is to advance the cam timing.
BTW, toolmanmike (or memike? ONE of those Mike guys!) has a lot of good documentation on the pistons. The EGGE 4 BBL L2222 replacements give the best CR versus the Kanters IIRC from Mike's work. (Correct me please if I am wrong...)
A local machine shop here also has worked over some old Ford 256 8 cylinder pistons for use in the 273; bore is identical and the 1.857 compression height means you can get a zero deck or above deck installation. Eyebrows are machined and the smaller pin diameter is used by bushing the Mopar rods' small ends. You end with a true 9.3 SCR with 57 cc chambers and the proper head gaskets IF the pistons heads are left flat; you can get even higher if you mill the piston tops with a dome left in the middle. SO a LOT of work,but you can push the Static CR on up a bit higher than the (actual) original CR. (And I don't know the end piston/pin weight to tell you what happens with the balance.)
The 3.625" bore diameter and pin height and compression height make the choices in other pistons very limited.
