[Jac Mac]

Ian,
One way you could overcome this problem with one set of headers to cover both options would be to enlarge the header flange to cover both port options, then with standard heads also supply a spacer port plate to make up for the effective width difference.
So on a 'normal' 302 you would use --headers plus spacers.
On a 347 with the above raised port heads-- headers only.

You would then have to ensure clearance in the collector area for both options, but this would allow you to have one set of exhausts only-- of course as soon as you do that some turkey will wander in with a set of 'Yates' heads.

Jac Mac