I've been trying to figure out what undersize nut goes on the backside of the bolt the fan bracket pivots on. I think I just figured out there is no nut there, just a cotter pin. Also, I think I may have the timing adjuster rod on backwards. Looks like the cotter pins are on the front side, towards the radiator? I'll have to check it out tonight. It probably will be easier to get the cotter pins in and out.
It depends what year Model T.
The timer rod has the cotter pin on the rear side for cars built from 1909 - 1911 that use the two piece timer.
When the aluminum oil filler timer came along in late 1911 the timer rod was bent forward where it goes through the timer, which is the way it was through 1927.
I might be trying to use an earlier rod on my '21.
And yes, make sure you install the cotter pin in the fan bracket bolt. Don't ask me how I know. At least I caught it before I had a destroyed radiator.