The old 404 will do much better than that. That sweet little overhead cam engine will turn to 5500 rpm when tuned right. Rated speed is 96 kph and they will do better than that. That rated speed was tops for Unimogs until displaced by much later models, and only if those later models have faster axle ratios.
If you keep lube in the portals they will never over heat. The transmission is the weak link, having two bushings that can starve for lube at sustained high speed.
Synthetic trans fluid helps a lot.
The tranny will last forever at speeds around 50. It's when high sustained speeds, like on a level highway, approach 60 that transmission failure occurs. Quick runs up to 60 plus don't hurt it, as for running down hill fast to help on the next hill.
The Petronics ignition will not make it run better than the points it peplaces, but Petronics will not degrade over time like points do. And, there is no dwell to set! With the shielded cables, the spark plug gap is only half a mm and fouls easily. The gap cant be increased or the shielded cables will break down at the higher discharge voltage.
If the original shielded spark plug wires are still on it, that and the dissy cap, and shielded plugs should be replaced with a civilian kit as available from Expedition Imports.
That and a carb rebuild should help immensely. Oh, you said propane, so my carb advice can be ignored until you swap back to gas
Your 404 will need some TLC but you will like the results.
