yep agaree with the fuel overfill or drain it is on ours...you need a pipe venting under the car to ground! Just like the oil breathers on the block.
2015-04-07 08.12.23 by
Robert & Ali Davies, on Flickr
I like the test bed, did you build that?
I don't know anything about these old engines but if the pipe attached to the manifold is open to drain, doesn't it affect the manifold vacuum or does it have a tap or one way valve? I'm curious.
BTW, I love the Flickr link to the rebuild.