YES. They will bolt right up.
yes
The headers for a 350 and 305 are the same.
If you are asking if you can substitute a 350 for a 305, the answer is generally yes.
no
No, Not even close.
The headers would be the same anyway, so you can order headers for the 83 and be all set.
yes it will
Yes
NO they are to big.
No, 350 headers will not fit directly on an Oldsmobile 403 engine. While both engines are part of the GM family, the Oldsmobile 403 has different exhaust port configurations and dimensions compared to the Chevrolet 350. To use 350 headers, you would need specific adapter plates or custom modifications to ensure a proper fit.
engine will fit, but 305 tbi will be too lean for 350 It'll burn up
Yes if its stock no headers?