That's a rochester quadrajet carb from a GM vehicle. Definitely not oe for your engine, but a common enough swap for 345's with either spreadbore intakes or squarebore using an adapter plate like the one you have. I ran the same setup for years on my 345-powered Scout, hooty...until I swapped a 392 into him.
The stock carb for a 304 equipped '69 800 would have been a Holley 2300 2bbl list#2977. Unless that's some trick rpt manifold, someone has swapped a 345 or 392 into your Scout.
One of the first issues I see is with the location of your throttle return spring. It should be connected to a point forward of your throttle linkage to provide resistance against the throttle rod. The way it is connected now, it is pulling with the throttle rod.
It also looks like you have one uncapped vacuum port on the front of the carb. That could be causing a major vacuum leak. It looks like the old rotten-ass cap is just laying there like roadkill on the intake manifold just below the port.
Like mayben says, we don't like to make assumptions, but with the amount of corrosion visible on the external carb parts, it's hard for me not to assume that the insides might look just as bad if not worse. Do we know anything about the history of this carb? Was it a j/y salvage?
How about a pic of the other carb you mentioned for positive id and comparison?
