I know your motivation right now doesn't include thoughts of selling it but JFTR there was a Firebird to Camaro conversion someone was trying to sell for an eternity on ebay, couldn't give the thing away. Still going to have a Firebird VIN and all. My buddy is a Firebird fan, likes them because they are different "Everybody else has Camaros!" I like the TA clone idea, that would be cool(plus I like the color scheme
)! Be a killer at cruise night!
Looks like you're looking in the right spot for the engine serial number ( 700616) and engine code ( X5).
The X5 code is for a '73 "High altitude" L-78 230HP 400 w/ Turbo 400 3spd auto put in a "A" or "B" body Pontiac. To be numbers matching the VIN number (stamped on the front, lower face of the block next to the timing chain cover way down low near the harmonic balancer) would have to match the cars, but if it is indeed a '73 X5 engine they aren't going to match. Bad news: non-numbers matching. Good news: you have a 400 not a 350, looks like you need to change your "drives" info.
Link to Pontiac engine codes
Don't know about '69, but in '67 Pontiac being a little upscale from a Chevy, they did a little more suspension work and so forth (i.e. the "radius" rod added in '67 to help with wheel hop, Camaro had only one on passenger side, Firebird had one on each side). So the Pontiac engineers did strive to make the Firebird drive and handle just a bit better than the Camaro.
Congrats on you new acquisition!!!