Sounds like re-doing another iron head is most cost effective, IF you can find the data or the original porter to make it flow the same. That is one issue to solve.... how to get the new head flow the same as the other one.
Your rockers and shafts ought to transfer to any new head(s), but we don't know what was done to get to that high compression ratio. The aluminum Edelbrock heads and Indy/RHS heads have much smaller head chambers than stock cast iron X heads, so unless the X heads were milled a bunch to get that SCR up to 12.6, then there is a compression ratio question that needs to be examined if you change to new heads.
If you like, post info on the pistons and any work done to the heads, plus head gasket numbers, plus cam info, so some better advice can be given on the direction for the heads.
Valve spring info would be interesting too.... it may be that the valve spring broke, and dropped the valve enough to let the valve head jam and the stem bend.. which got pushed up into the guide crooked. You may see the chamber cracked when you pull the head. If any valve marks are on the piston.... then the rod needs examination and maybe even the crank. If the piston head is free from any valve marks, then that would be good.
I'd suspect that there is at least a little coolant in crankcase; if it gets out the plug hole, then some is very, very likely to seep past the rings.
