Yup, just plug the vac. line at the manifold. I would check the insides of the dist. to make sure it's all solid (nothing flopping around. You will still have the mechanical advance which should help when starting. Make sure you have 34 - 36 deg total advance. It should be all in by 3K rpm.
I think you will see a noticable improvement if you put a Performer intake on it.
Can you call the folks who built the motor and find out what cam it has? I agree, you should be seeing better than what you're seeing. The cam can make a huge difference, even with lousy intake and exhaust.
When I built my motor, I used the cam recommended by Mondello. It ran about like yours. I called Mondello and told them what I had and that I expected a whole lot more for the money I spent. They sent a new cam and lifters. I made the change and it was a lot better. I'm NOT saying that you're have the same kind of deal......but.....who knows. Gotta start looking somewhere.
The builder should be able to say what power should be available, or at least a range based on carb, intake, and exhaust selection.