To clear up one issue.
9777641 was the Service Replacement p/n for the '67 GTO RH HO exhaust manifold. It is the p/n you find in the Master Parts Catalog.
An example of how you have to know what you're doing when using the MPC to research OE p/ns.
The CASTING itself was p/n 9777642, the p/n you will find on manifold itself.
PMD ONLY serviced the RH manifolds as an assembly including the Heat Riser Valve. The assembly required a unique p/n, that is true for all of the RH manifolds in that era.
PMD eliminated the trouble prone HRV early in the '68 Model Year on the standard log manifolds.
To the best of my knowledge, up to a point the '68 GTO HO/RA continued to get the carried over RH manifold. The '68 did get a new LH HO manifold, p/n 9791637.
I do not know off hand if the elimination of the HRV resulted in a revision to the HO RH manifold. The elimination of the HRV resulted in a new p/n for the log type RH manifold (pretty sure about this, I used to thoroughly research the log manifolds but going by memory at the moment).
Like the LH manifolds, the new RH log manifold was no longer an "assembly", so was serviced by the same p/n as you find on the casting.
The first gen 'birds used the same HO manifolds as the big Pontiacs, they did not share with the GTO (A body).
In '70, the F Body was able to share same manifolds as the A body (both log and HO/RA).
The round port manifolds are a separate discussion.
I'm a little confused as to what you are saying when you say "these" are 4 bolt holes being GTO repops vs 3 bolt holes being Firebird.
OPH posted the hole count for the "flange" to head and also the bolt count at the outlet by Model Year. Matches what I know about it.
Your pix show 5 bolt holes for the "flange" to head and the p/ns are correct for the '67 GTO application (and '68 at least until they eliminated the HRV).
The first gen 'birds used the big car HO manifolds as I mentioned. These had 6 "flange" holes and 2 outlet holes.
The '67 used 9779495 for the LH and the 9779494 for the RH, with the same confusion as for the GTO since the RH was an assembly with the HRV and in the MPC the service p/n shows 9779493. You'll never find a manifold with this p/n on the original casting, only 9779494.
The LH stayed the same thru '69. The RH got a new p/n when the HRV was deleted and another in '69. I believe the flange and outlet hole counts were unchanged however at 6 and 2.
OPH has a lot more parts experience than me so if I stated anything incorrectly, I'm sure he'll be able to offer a correction.
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