Face palm... I'm not saying anyone is giving you bad advice here, but since the boat already out of the water you have a great opportunity to just nip the problem in the bud before the hull touches water again. The Catalina Smile alone is enough to make me believe there is a possibility of water ingress. The job isn't as hard as people make it out be, then expense involved is the yard and the lifting equipment... since you already on the hard, that expense is already drastically reduced. I'd negotiate at least an extra month to 6 weeks of dry storage time to be included by the seller, giving you enough time to drop the keel, fix the stub, re-bed with 5200 and allow to cure, re-apply barrier coat, bottom paint.
I'd do the job for free just to prove it can be done cost effectively if I lived near you... given that yard you are in allows DIY work.
BTW, that CD kit is horrible... Stainless LAG screws couldn't be torqued effectively, they'd snap off. If an owner wanted to use extra bolts as a retrofit I would drill and tap for proper 1/2" or even 5/8" bolts. Lead is so soft it will tap nicely without using cutting oil.
