Given the aftermarket aluminum heads out there now and the cost to rebuild a set of 308’s I would think that they’re not nearly as desirable as they used to be. I would think those racing classes that require stock heads would be about the only market.
I mean I have a set of ported 308’s on the 340 in my Duster. And knowing what I paid to have them done, even like 10 years ago, there’s no way I’d rebuild and port a set of 308’s vs just buying a new set of aluminum heads.
I feel like they fall into the same category as a lot of the later, stock upgrade parts. At one time you could junkyard dive and hunt down stuff like the 308 heads, and 11.75” brakes, police spec bars etc, etc. And they were and are an upgrade over factory A body parts, but, the aftermarket has long since surpassed the levels of performance they can provide.