Really you would have been better leaving a small gap between the base frame plate and the column plate then fitting some grub screws in the Coloumn base plate so you could set the coloumn true. This way you can fine tune the column with the rails etc fitted using proper setup tools like dail gauge's rather than cheap set squares which are just not accurate.

Then when it's all setup fill the gap with Epoxy metal putty, spray the coloumn plate with a release agent or tape the surface and you can still remove when needed. This process works very very well when you can't machine the surfaces.

Edit; Oh and the music on those Vids is annoying ASF...