Do yourself a HUGE favor and subscribe to Car Craft magazine. I get it for $10/year.
There is nothing too difficult about swapping out a manifold on a small block Chevy V-8. (It's NOT a six cylinder because 2bbl carbs didn't come on those). It's highly unlikely that the engine would be a big block. Again, I don't see many BB Chevys with 2 bbl carbs.
If it's the original engine, I'd guess it's a 283, 307, or 327. After 43 years a 305 or 350 could have been swapped in. Changing a manifold on any of these engines is the same process.
"No one is useless if they can still be used as a bad example." ~ SSgt. Miller.
"Loud pipes lose rights."