Slant 6 offi 4 barrel intake

Offy first offered that manifold back when there were still WCFB four barrels around, and it will take a WCFB four barrel as is. Maybe some early AFB's, too (I remember the hi-po 273's carb base had extra holes so it could mount to the 273's intake). You need the adapter for a modern AFB, Edelbrock or Holley - all of which have a larger base bolt pattern.

Those old WCFB's didn't flow many CFM's and they would actually work pretty well on a slant six if you could find a good one.

I'm pretty sure the throttle bores in the OP's manifold have been opened up. Been a while since I had the carb off mine for a look see.