10.5:1 273 pistons with 360 heads compression ??

Well this is where I was saying estimate and using published numbers. 360 valves clear. I don't see how 10.5s and open chamber would end up with low compression just not sure where it would end up. I am using a small bore thin gasket as stated. I don't know deck height as I got the motor and just replaced bearings gaskets heads cam (normal rebuild stuff) but the pistons measured .003 down in the bore and yes they have 4 valve reliefs. I'm assuming the deck was cut as most 273s I've measured are -.015+ down in the bore.