Several things come to mind,
-Need to look at the casting of the cylinder head above the #1
exhaust port. Any evidence of grinding? Or a small stamped 722 or 614? If so, you have a pair of Service Replacement RA IV heads. The heads could also be pair of 197 '71 HO heads, will have a small raised 197 above the large 1 cast into the #1
exhaust port. Will also have an X cast to rh of the bolt hole in the center exhaust port.
-SR 614 RAIV heads were first Pontiac castings ive ever noted cast right after the Fall of 70 UAW strike (near 60 day strike from Sept 15- mid Nov of '70). Had a pair many years ago cast by Pontiac central foundery in late Nov of '70, they were also the first externally dated round port heads. SR 614's should have the X on the center exhaust port to the rh of the bolt, will also have the large C on the rear exhaust port, same as '71 197's.
-above the center exhaust port area, to the left hand side in the recessed area, is there an alphanumeric date code? Example L020, L080, A080? Those 3 dates are the most common dates on late style '71 455 HO heads, 197's. Early style '71 197's had no casting date. Have original sets of both styles on my '71 cars.
-Original '69 & 70 RAIV heads as well as early 197's did not have a cast date on them externally. Originals had a date cast, but it was under the valve cover where the head was machined for the exact center head bolt. When the machining took place, the majority of the date casting disappeared.
-All late roundport heads ('72 7F6 heads & '73-74 SD heads) have a fitting or temperature sending unit screwed into the side of the head.
By examining the heads carefully with above info should be able to narrow down what you have.
The exhaust manifold casting # is '70-72 driver side roundport Am struggling with noting exact date code, am on an old IPad.
Would be interested in the casting date of the block if you don't mind sharing. Thanks!