Are they .042" gaskets and .032" thickness instead. 3 or 4 thousands is a little thin. Possible a mixed gasket set of left overs was installed. Personally I dont use shim type gaskets either. Factory commetic are good , do not like the shims.
No it is not common to have the sides different. Yes you can do it .
Exhaust in the coolant? You CLT it and found bubbles in the radiator. How did you check the block. Are the heads off, if so did you flux them.
Blowing the radiator hose off is from the supercharger. I run 10 psi on a 305 and although my heads have no cracks, I cannot see this happening. How much boost are you using?