I have now received all parts related to the shift drum replacement/upgrade.
My engine is still very much apart but I have the transmission, shift drum, shift forks and shift shaft mocked up in the right side case half. Recall that the ‘87 drum I purchased had a smaller pattern for the “star”, well the ‘87 shift drum/star wouldn’t work with the ‘85 shift pawl- the pawl would catch the ‘nub’ on the shift ‘star’ But would slip off before making a positive shift. Luckily the late KX500 shift pawl is still available new.
Kawasaki part number 13165-1122 PAWL,CHANGE LEVER —$12ish usd
I received the new shift pawl yesterday and compared it to my ‘85. The claw ends of the late shift pawl are closer together. With the new shift pawl installed it now rotates the drum as intended and the transmission shifts gears.
According to microfiche on partzilla the shift drum assembly and shift pawl are the same part numbers from 1987-2004 KX500.
I believe the late KX500 shift drum is a viable replacement for the ‘85 KX500 and likely all pre-1987 KX500. I will give a definitive follow-up one my engine bottom end is back together.