Don, what are you using to measure draft, the 460 that came with the boiler?
I have two Dwyer 25 manometers. One in the flue before the baro, and one over the fire.
I drilled and tapped a 1/8 male x compression adapter into the smoke pipe and installed a NPT locknut, then ran 1/8" OD copper tube almost to the manometer then adapted the hose using a 1/8" compression x insert. I did the same on the bottom by drilling and tapping the inspection cover. A locknut isn't nessassary here because there's enough metal to keep things put.