A little update.
The bike is running well now, although I haven't had a chance to ride it.
Back story: I messed around & messed around trying to get it to run - tried different jetting, two different carburetors (a CV & a flat slide), poked & prodded, rechecked this, reset that & basically just got frustrated. Also, every time I checked the timing it was out a fair bit. I finally concluded that I was the world's worst mechanic & I didn't even know which end of the screwdriver to hold when I was pounding the pipe wrench. I gave up & took the bike to a local expert on old H-D's & asked him to make it run. Well, long story short, he found that the #2 cam gear was slipping on the shaft & letting the timer gear get out of time with the cam. So every time I timed the mag, as soon as the engine started, the gear would slip, timing would go way retarded & the bike wouldn't run. No one's fault - just a freaky oddball failure that no one anticipated.
So now it's running pretty good. I haven't ridden it yet, but the mechanic did & he says it goes like stink.
One other related issue that I've learned something about in all this: The M-74B nozzle will NOT work in the M-53. The reason is that the M-74B nozzle is much longer than the M-53 nozzle & when you put the longer nozzle in the M-53 the bottom of the nozzle blocks off the main jet opening, where it goes into the center bore where the nozzle lives. The reason the M-53 nozzle is shorter is because it seats against a shoulder that is machined into the carb body, at the top of the nozzle bore. The M-74B nozzle goes up higher & seats against the bottom of the annular groove in the venturi, quite a bit higher than the feature on the M-53.
Unfortunately, I have not been able to do much more lately because I've travelling a lot for work, but my plan is to make the race at Gingerman at the end of August. Keep your fingers crossed...