How much power/ what would I gain with a 350 intake on a 307 5a engine?

 

Stock iron 350 intake? Zero.

Do you intend to change the carb and distributor to non-computerized?

For an otherwise stock 307, get a Performer (not RPM). Keep in mind that the entire package needs to be matched.

 

The 5A headed 307 is just over 8 to 1 compression with a tiny cam. If you have an A4 factory aluminum intake, save your money for something like 2" or 2.25" dual exhaust and the block off cap for the manifold, that will actually give you a performance boost.

 

If you really want a performance boost, go for a set of gears.