I agree for the most part in what has been written:

Just for fun, I'll mention just how difficult it was to get and keep the old DeJur Professional 4x5 enlarger in any kind of alignment, let alone square. I share this only because I have paid my dues in money, blood, wasted paper, chemicals, sweat and tears in attempting to maintain some semblance of sharpness corner to corner with the DeJur. :-) I thank my lucky stars for Omega and Besseler.

I have had no trouble over the years of using the simpelest enlargers for the corrections being discussed. A film holder, a roll of film etc. all serve as tools to aid in tilting an easel. Really pretty simple and straight forward. Some times imagination can be one of your best dark room tools!