Yup, slip off the rear cover after removing two screws. These are 0-30 in Hg / 0-100KPa gauges from McMaster-Carr. Stock # 4002K14.
I used a tee and then a syringe to pull a vacuum when matching the gauges. For the restrictors, I drilled a very small hole in a length of 1/4 " wooden dowel and then inserted it into the larger diameter tubing. I was hoping the 1/8 " tubing would create enough damping, but no cigar, so I added the larger diameter 1/4" tubing and restrictors. This is basically a prototype. You can improve on it, I'm sure.