It should be approximately 90mm from the ground glass to the lens flange when focussed on infinity. The nearest focus you can use with any lens is dictated by the amount of bed and bellows draw you can get. The more you move the lens away from the ground glass, the closer the focus is. The nearer the lens is to the gg, the further the subject is (ie infinity).
If there are no markings for a 90mm it doesn't mean you can't use it, they just may not have had room to extend the range from 90 to 240. The other option of course would be to use a recessed panel. A 30mm recessed panel would give you a front standard to gg distance of 120 (90 + 30).
This has the advantage of drawing the bellows out allowing better movements because you are not restricted by the bellows. I'm not sure if the 45CF takes bag bellows, the 45AII doesn't.
If you use tape, you will have to be careful not to restrict any movements. It might be better to use an indelible pen?
Enjoy your new discovery when the lens arrives!
If you need more advice, just pm me.