Zero Compression after head gasket replacement?

Changed head gaskets as old were seeping oil. Compression was normal when done.

Used Fel-Pro head gaskets and torqued by the instructions. Lifters do not require lash just to be torqued to spec.

Engine backfired once on ether and then gas down carb but no start. Found timing was 30 advanced so backed off to zero. Still no start.

checked for compression #1 and next cylinder and had zero. Engine sounds like running free when starting.

removed valve cover on one side and valves are all opening and closing. I do need to check both valves are closed at #1 cylinder when at TDC was too cold to do yesterday.

This engine has sat for about 2 months open to the atmosphere although I did spray down the cylinder walls with WD40.

This is a Ford 400 engine and all that was replaced was the head gaskets and intake. The dizzy did have to be pulled and it did not go in exactly where it came out (30 degrees advanced) and this is when it backfired.

Is this a case where the compression rings are no longer seated properly? Will something like a Seafoam treatment down the plug holes over a few days will help? Evidently this does happen I just would not have expected over a couple of months.