[60sstuff]

Some helpful pics for what it's worth - 65 and 66 would typically have this brass ell fitting coming off the front carb base. Factory slotted plug installed without power brakes and a power brake car would have a short steel line threaded into the ell that would meet with the steel vacuum line from the P/B booster held together with a clamped hose as seen in the old magazine pic.
I have seen another style brass ell (bigger block design) also used with a different cap plug.