Timmer,
Interpreting vacuum readings is sort of a science. I am guessing that your source for this
information was indicating this test would be a
benchmark of your engines health.
I am not "vacuum wise", so I am not much help in regards to your specific question. If your engine is good condition, the two carburetors will give you a noticeable increase in power.
The vacuum test might be one way to check...but not the only way. If your rig starts and runs fine, doesn't burn a quart every 10 miles and can cruise down the road without laying down a smokescreen then it is probably a fine candidate for the two carb setup.
Stuart