If you tightened the plug and it still blew out, the threads are likely beyond being repaired by running a tap in there, but as the cheapest and simplest option - it's worth a try. Realistically, you will need a helicoil insert.

My son's 81 came to us that way, but it seems the shop that installed it didn't get it right and it blew out while climbing a long grade. Now it had a big, non-"coilable" #2 hole. Off with the head and to a specialist shop (Central Coast Cylinder Heads, Atascadero, CA). $250 later, IIRC, it was back with welded and rethreaded plug hole, new valve seals and hushers, all valve clearances adjusted, red-painted combustion chambers(!), a new cam oil seal, and so clean you could eat your dinner off it. I wanted to put it on the coffee table, but son needed the car.

50k+ mi later with no head problems. Not a cheap fix, but the right fix.
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Bob (son's 81-244GL B21F-M46, dtr's 94-940 B230FD, my 83-244DL B23F-M46, 89-745(LT1 V8), 98-S90, 77MGB and four old motorcycles)