TBKBABABTIM, I'm at a very similar stage to you in my build and have just attached the bell housing / gearbox to engine (Sigma). I too put sealant around on the paper gasket, not sure if was needed but remember reading somewhere to put sealant round bell housing to engine, the build manual didn't seem clear, so I did it anyhow.
It all went well but so far just can't seem to get at the inside bolt which attaches the starter motor to bell housing. If you solve how to tighten it please let me know (I was just going to leave it for post build check otherwise).
Hope your enjoying the build, this is my first attempt at anything like this and feels like doing a massive puzzle, it's amazing how one simple sentence in the manual transcribes to hours of fun.