oooops on Piston choice

It sounds like the cam's just too large for what you have. You based the choice on the want, not what they delivered. If it's a street car, I'd just leave the lower end and revise the cam choice. KBs are much lighter than the pistons you're likely to have if they sit that low in the block. So you're talking about new pistons, removing the old pistons they'll be pressed pin (again based on the "short" compression height of cheaper pistons) , balancing the assembly, pressing the new ones on, a quick touch up on the hone, and new rings. I'm not sure a couple points of compression are worth the work if the rest of the engine is good. Swap the cam to something with 10* less duration at .050. Maybe a solid lifter if you want a little more torque off idle. Then run it and enjoy.