I have two Omega DII.
I tried aligning it with a carpenter's level and a plate of glass. What I found frustrating was that I level something once and come back to measure again, the level shows it is now out of alignment. Did this for a few days... trying to do it in two axis at 3 different planes and having it to agree on level was nearly impossible. I finally got it and used it like this for a while.
Then my girlfriend bought me a Versalab's laser alignment tool. It took me all 30 seconds to find out it really wasn't aligned right. Took another 30 minutes to align it correctly. (remember this is my first time using this tool). To recheck it takes a minute or so. I then aligned another one of my D-II in about 15 minutes.
Based on my experience, I don't suggest using carpenter's level. When I tried it, I couldn't be sure what I was reading was right. (and it wasn't)
I know Beseler has a dedicated level for this purpose. It's $179 at B&H. I'm sure you can align it correctly with this jig as something like this has been in use for decades for this purpose and all masters used something like this in their setup.
Versalab, by the way, is $189.
To me, the choice is clear.