Time for cheap plug
IF you had
The Savage Companion Photo CD, you would possess some photos that were submitted by Kropatchek. They show the inside crankcase halves for the 5 speed model.
Noted on those photos are the fact that the shift drums between the 4-5 speed models are different. The 4 speed had 1 shift fork whereas the 5 speed has 2 shift forks. Those forks are supported (of course) by bosses that are cast into the crankcase halves...
Therefore, the countershaft, drive shaft, shift drum, shift forks, shift mechanism, crankcase halves, primary drives AND alternator (German_Leo) are ALL different. Don't know about the oil pump drive
The possibility that I imagine would be to see if the '86 alternator stator and pickup will fit the later model rotor and then just change over the top end with head, cylinder, and piston etc...
BTW - anyone know if the cam drive and driven gears are the same? Need to check Ron Ayers maybe.