The instructions sound right to me. I use Jobo tanks. The 35mm tank needs roughly half as much liquid as the 120 tank. I imagine this applies to most tanks so the Fuji-hunt kit instructions are about right. I'd expect use twice as much liquid for 120 as 35mm so I could do half as many 120 films as 35mm films. OK in a Jobo tank it is possible to put two 120 films on one reel and thus do the same amount of films as 35mm but Fuji- Hunt are basing its instructions on one film per reel.
If your tanks will only take one film per reel then it is likely that the amount of liquid to cover the 120 reel will be roughly twice as much as to cover a 35mm film. If you can fit two 120 films in the same tank then you can base the number of 120 films that the kit will process on this.