I have installed one in my beseler 23c (original, not III ). Not sure if it will be the same, but it is very straightforward. The cold light head slips in through the filter holder and the top of the upper bellows slips right over it.
Here I will offer some extremely obvious advice. I rewired the ballast and installed a new switch for the light. The original connector that goes between the head and the power supply had been cut, and when I re-wired it, I was so intent on doing a good clean job w/ the high voltage lines and making it safe that I neglected to feed the wire through the top of the enlarger housing before I put it all together. So mine comes out through the filter holder door, which is less than ideal. Eventually I'll add a new connector and thread it back through the top of the enlarger ( where the cords originally would have gone to the condenser lamp. ) You won't run into this if the connector is OK.
I check APUG often and will keep my eyes on this thread... if it would help for me to take photos or whatever, I will. There were several versions of the zone vi cold light head and mine is one of the earliest. I also figured out the photodiode wiring and monitored the light output... if yours is the older one like mine, I've got some tips for getting consistent exposures without a compensating timer.