It's likely to be a vacuum take off point for a brake servo. Sometimes there is a non return valve screwed in the manifold at this location.
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!