n = 1 (depending on how you count them).
I decided to reassemble my Porsche mountain bike frame into a usable bicycle. It'll have (mostly) period correct but not original matching parts. I've even got a couple of trails in mind, one that I can ride to from home, that I'm not afraid to ride. Unfortunately, the assembly process is at an impass.
I can't do the drive train because I don't have the right bottom bracket. The Porsche has a 68 mm BB shell. An easily solved problem and not too expensive, but it'll delay me for another week or so.
I can't do the brakes because my fork doesn't have any spring retention holes for V-brakes. I was going to kluge a solution but my machinist son advised against it. He thinks that he can acquire a set of stops from a friend or, if necessary, will make me a set. I actually have a set of Magura hydraulic brakes that would work, but I've gotten rid of most of my hydraulic brake stuff and I don't want to mess with them.
So seat, handlebar and rear brake are pretty much all that I can do today. That's OK though. Actually, I kind of like thinking through the process. That's part of what I like about working on bikes that are a bit out of the mainstream.