NAPA website is good for looking stuff up by application and getting photos, specs, etc. I expect it will take a trip to the store to physically look at the thing to see how it's made. 3/4 nipple with 1/2NPT threads is the typical deal. Late 70s-80s GM used them on their AIR systems as well.

The breathers are not all the same. The breathers Moroso sells for the Vac-u-pan are different from the ones used strictly for a vent. Looser I believe to allow the system to be more efficient. At least that's how it used to be.