When the pistons are are TDC they are extremely close to the top of the block, could be between 1-2mm below but not a lot. What did factory clevos come with, a lot less?
The gasket thickness must also be a consideration with compression. How thick are they, I have never measured one. I'm assuming Felpro gaskets are thinner than a standard one. I have heard you can use two gaskets if you want to lower compression by 1 (ie from 11:1 down to 10:1) Not willing to try unless I know it works!!
I think LPG varies from 98-105 Ron so if your 351/302 heads went OK on pump fuel (96-98Ron) I should be fine with LPG and Premium unleaded when I run out of gas.
What cam do you think would be suitable with this setup and reduce compression, I am looking at 270 inlet duration and 280 exhaust duration.