OP, those pistons look like Keith Black KB243's. The step of the KB's is going to be around .020" to .040" high. You can check by sighting across a feeler gauge and the piston top, with the gauge placed on the outer step to get an idea of how tall this step is. Also, look at the pistons from underneath to see if you can see any markings around the pin bosses.
With that PT8553 head gasket and unmolested head chambers, your static CR (SCR) computes to be around:
9.2 for the KB's
With your present cam, and assuming it is installed with no advance (as it looks from your pix with no extra crank keyways), then your DCR (dynamic compression ratio) will be:
6.8 for the KB's
The KB's and the stock head chambers have low enough DCR to totally explain your lack of low end grunt. With the cam like you have, you would have to advance it a crazy number of degrees, like 13 degrees, to get the KB's DCR up to the mid 7 range. And for really good torque, you need to get it up even more.
IMHO, with this info, I think it is a 100% complete waste of time to advance this particular cam for what you want to do with the car. I would recommend a new cam like you originally proposed doing. You need IMHO to find one with an intake
closing angle of 60 degrees. This can be found on the cam timing numbers published in the specs. You can see that kind of intake closing angle here for the XE268:
20-223-3 - Xtreme Energy™ Hydraulic Flat Tappet Camshafts
Also, since in another thread, you indeed seem to have coolant leakage. This would be a good time to not only have the heads checked for warpage, but also have them milled maybe .010". That, with a Felpro 1008 gasket, is going to get the
SCR with the KB pistons (IF that is what you have) up to around a true 10.1, and the DCR with the XE268 cam will be around 8.1. That is all gonna make a HUGE difference in low end torque. And that is as far as you probably want to push
up the DCR to keep the tuning reasonably easily to run on pump fuel.
There are other combinations of head milling and head gaskets and cams that will get your DCR up to this range, but that is where you need to be heading for straight low RPM street use.
Again, check those pistons to see how high that step is to be sure what you have there. From those pix, that is my best guess of what you have.
