Newbei 67 Plymouth belvedere 318 2bb dist vac port is timed or full.

FBO (4secondsflat.com) says use manifold vacuum (drivers side)
They are pretty much race oriented and the owner Don Gould took 2016 King of the track Madras speedway drags.

That said, a lot of us use ported vacuum for the average daily driver street car (passenger side on your 1406)

This tuning book is a must in my opinion for people who want to learn more, and is probably the best 20 bucks you will spend on your car.
Performance Tuning Guide