I fogot one tip: the obelisk post is 342 mm tall, and the mirror holder here is 8822-UHV, which is 34.9 mm from the bottom to the assumed mirror center, while the height of the suspended optical table (set by VIS) in the PR2 chamber is nominally 380 mm from the top surface to the interferometer beam line. So a spacer with 3mm thickness should be required inbetween the obelisk post and the mirror holder if you like to "more precisely" tune the height.

In addition to that, please note that the main beam flys with launching up around PR2 at the rate of 1/300; considering this fact, let's say we would need to add 5 - 6mm in total if you might like precise life, as the post would be ~ 70cm away from the center of the PR2 mirror.

About the dirty, I'm sorry but I can say I knew this would happen from the first; as I learned the PR2 chamber won't be in vacuum in phase 1, so I asked to omit vacuum comaptiblilty and got it auickly with inexpensive cost.