Interesting that Pontiac V8's stopped using the Nylon Coated timing gears in the early 1970's. When I replaced the cam on the original Buick 350 in my fathers 78 Catalina Safari a couple of years ago (before the rod bearing spun) it still had a Nylon coated car sprocket.
AT5 stamp I was given a possible other explanation by a long time Pontiac Engine plant Cold test engineer. He didn't start until 1981, so his experiance is only with 301's & Iron Dukes, but he said that they would randomly Hot test a few engines a week, and they would be hand stamped AT# for assembly test and the number the test engine was, in this case the 5th one of the week. He says he can not be sure that is what it means though.
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Jeff R
60 Jaguar Mark 2, 3.8L Automatic
67 Sprint Firebird 230 OHC-6 4-Speed A/C
78 Catlina Safari, Pontiac 400 powered
77 Astre Formula, 215 Buick V-8 T-5
73 Lemans Safari, 400 4bbl 4-speed
71 Catalina Enforcer, 455 4bbl
06 Mallet Solstice #024 LS2, Now with a Tremec 6060 6-speed!
2012 F-150 Echo Boost (My local Ford Dealer SUX!!!)
2020 Dodge Charger Scat pack (recovered)
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