Head gasket hell
I thought so,it did get pretty dirty while cleaning would radiator flush work to get the gunk out of there is some.
Rad flush is a waste of time & money, & won't do a damn thing to remove debri/gasket material. Drain it, pull it, turn it upside down & get a garden hose hooked up to the lower hose neck seal it somehow & let it rip. That's the best You're gonna do rad-wise on Your own, might do the reverse-flush on the heater core while You're at it. If You stirred-up junk in the bottom of the water jackets, You may want to hook Your garden hose to the heater hose on the head, then let it rip out the lower rad hose.
If the flow thru' the rad can't keep up/doesn't clear, it probably needs rodded/replaced.
As AJ alluded to, be sure Your vac advance is hooked up properly & working, and as also mentioned above,....please be mindful of where the antifreeze is going. I'm always keeping track of the feral & neighbor's cats & other animals, & cleaning up after Myself, as big a PITA as it is sometimes...
Good luck & keep Us updated.
P.S. It would be impossible to flip the gasket end-for-end, the dowel pins are staggered, one nearly at bore center & one offset almost to the side of the front bore camshaft side.