[MrPbody]

For some odd reason, I can view the pics up to the last body shot. I can't see any of the engine bay or interior. It may be something with my computer. Don't really know.
If it has a column shifter, the VIN should be checked to be certain it's not a "clone". I don't recall seeing any column-shift GTOs before '67 (that doesn't mean they don't exist, just that I've never seen one). The "237" at the beginning of the VIN is of no help, as it indicates "LeMans", which GTO was an optional package on in '65. If it's a "236", it's a Tempest. You must submit the entire VIN to Pontiac Historic Services and get your "build sheet". That will tell you if the car was ordered as GTO or it's been "cloned". Clones have become fairly common. In general, we (restoration people) don't have a problem with that UNLESS it's being sold as the real deal, and "clone" status not stated clearly. There have been recent court battles resulting in fraud convictions for those mis-representing GTOs that are really LeMans or Tempest bodies, rebadged.
TH350 was introduced in '69. It "fits" wherever ST-300 was (including driveshaft length). The transmission is easily recognized by the shape of the pan. ST-300s and TH-350s all have a rectangular pan with a corner lopped off. PGs say "PowerGlide" on them, and have a "complete" rectangular shape. ST-300s don't say anything, except the ID stuff on the tag. TH-350 will have two distinct "detent slots" in the forward gears (when you move the shifter, you'll feel them) and a detent cable, unlike any of the others. TH-400 pan is shaped somewhat like Texas or Ohio, very different from the others.
Another book to get is Jim Hand's "How to Build Max-performance Pontiac V8s". I may have already mentioned this, but it deserves to be said again. It sheds a lot of light on the myth and superstition that abounds in this hobby. Jim managed to get his 4,100 lb. LeMans wagon into the low 11s on 93 octane with a hydraulic flat-tappet cam. He offers over 20 years of trial-and-error, regarding building the monster for street use. Accurate and well written.
For more Pontiac-related stuff, go to:
performanceyears.com
boyleworks.com (musclecars)
classicalpontiac.com

All three of these sites are dedicated to the Injun, and have very good forums. Best of all, nobody there will tell you to "just put a Chevy in it".