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
NO they are to big.
yes it will
engine will fit, but 305 tbi will be too lean for 350 It'll burn up
Yes if its stock no headers?
NO. Not even close.