Quick question:

What are the stock sprocket sizes (front andrear)for the ironheads?

 

Drum brake (rear) models front 23 or might be 21 in rear 51
in disk brake models ( 77-&gt front 19/20/21 and back 51
These are just quess

 

The rear drum brake sprocket is a 51 tooth for all models.
The countershaft sprocket varied depending on the model. This sprocket came in 19T through 24T. You can barely get a 24T on the bike, but it will fit.

The 1966 and earlier XLH had a 21T sprocket. (The 1967 XLH & XLCH had this as an option)
The 1966 and earlier XLCH had a 20T sprocket. (The 1967 and later XLH & XLCH this sprocket was standard)
The 1970 & 1971 XLCH came with a 19T.
The 1970 to 1973 XL & XLH came with a 20T.
The 1973 XL, XLH, & XLCH and later (read that as 1974) came with a 21T.
Not that simple, is it?
From 1975 on, I have no idea of what the sprocket sizes may have been......pg

 

I'll complete the listing for the later Ironheads:
I believe all '75 thru '81 models had a 21 front and a 51 rear. '82 thru '85 had a 21 front and a 48 rear. I have an '83, and a 22 front just barely fits. A 23 front (which I'm currently running) requires some grinding of the sprocket cover mounting bosses to fit. I wouldn't even try a 24, and that's too large for a street bike, anyway.