Jens,
Original: Jens Eirik
Dar..
The old 4 stroke engine are reliable with modern glowplug, but the major problem glowplug for 4 stroke was not always available in first period.
I wrote exactly that, in my post #9...
Besides, I don't think even the Surpass and the Surpass II engines can exchange all their parts, with one another.
The pre-Surpass, probably even less, although some sizes may share bore and stroke specifications.
Even bearings are of different sizes (Old .40FS and Surpass II are the same, but the Surpass has a different size front bearing.).
Also, see the OS time-line; some engines had the camshaft in the front and others in the rear. I am sure that you don't think they can all interchange parts with current all-front-cam series engines.
The newer carburettors (I have my doubts about the FL's) work better too.