I work for a Mopar dealer and back when R-12 was king, we would have to use a vacuum pump to clear the a/c system of water. The pump would pull up to 29" of vacuum which is high enough to boil the moisture out of the system. The a/c machine we use now is a recycle machine with a built in vac pump that still pulls 0up to 29'. My guess is that if the Harbor pump will pull 29 then that should be suffecient, but I don't know what resin vac formers pull down to.
Great looking mock. Paint will be sweet iffuns you keep the color you chose. Hate to be a peckerwood, but I kinda like the nose down look with a body that looks that long with a roof that high. Feel brave? Chop it and then the tail-drag would look good. Hate me or not.