Highest flowing sbm heads?

The set I have on now were ported over 10 years ago and are an old open chamber style. 5.97 so far with not as much as a jet change. That’s a 9.30 or possibly in the 9.20’s. My car is honestly not a go fast combo with a 14-32 slick and is set up for bracket racing not test n tune or I would 10 inch M/T radials on it. And hit a coastal track like many.
John you say your duster is not a go fast combo, does it have factory front frame rails? Inner fenders? Firewall, backhalf car sounds fast to me