They're GSL-SE Housings. If you can find 13B housings with coolant seals in them, oil injection ports, and factory-cast blocked off coolant passages that didn't come from a GSL-SE, I'll give you an e-dollar.

 

Crit, he's right. Those aren't GSL-SE housings. Those are newer housings with water seal grooves cut into them. There is a threaded boss for a knock sensor above the trailing plug holes in the housings in the pictures. Also you can see the "bumps" on the top where the tension bolts pass through. You don't see those on SE housings and also look at the air holes below the exhaust ports.

 

Ahhh, dammit. I remember reading that part and re-forgot. I'll go hide now. Now I've got to dig out that e-dollar.

 

I like the idea, especially if the groove could be cut in the ground 13b housings. The housings always flake and de0chrome on the edge, so this is pretty cool. I guess once the 12a housing stockpile is totally gone this may become much more common. And, as mentioned earlier, you already have ported exhaust.

 

Continue here.
New organized thread with proper title

https://www.rx7club.com/1st-generation-specific-1979-1985-18/my-12a-blowthrough-build-up-725724/