If you can give us the results of a vacuum test at idle, I think there'll be some good clues there. A leak-down test will be good also, but I think a plain old vacuum gauge reading is easier for most folks. A leak-down test will not show bad valve guides whereas a good vacuum gauge probably will. If you have a liquid filled vacuum gauge it will dampen the bounce effect of the needle at idle (which if it happens will negate any sort of idle vacuum accuracy). If you have a non-liquid filled gauge and the needle at idle is bouncing back and forth like crazy, try pinching the hose. That will normally cause you to get a more realistic reading. Back when these gauges were more universally popular (hence engineered better and made in the USA) most of them included a restriction but the ones I see today (from a country with five letters, beginning with the letters Chi which is not Chile) just ignored that kind of thought. I attached an image of the connection spot for a Helicoid brand gauge so you can see. Hope it is helpful.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
