How to identify old ESO & JAWA engines?

[Dutch]

I have a list with Jawa 2 valve serial numbers by year from 1966 till 1978, but how can you find the production year of Jawa and ESO's made before 1968. For some time the year number was given as a part of the engine number. When was this practice stopped (maybe 1968?) Does anyone know the engine number or year the side drive cases changed from 6 webs to 8 webs. I am specialy interested in all the small different details from old ESO engine, like rocker valve cover, cooling fins on the barrel, etc.

[Freakshow]

Early one have the wide fin at the bottom for undoing the head.  and i think the numbers are cast on the side i know mine does have 72 on it.   Also the ealry ones dont have the cross drilling in the head for the oil to run back arcoss to the push rod tubes, so you can see the 2 little lines on the right side near the oil union bolt that indicates that.

Obviously the cover has the bolt on eso plate too and also the case cast webs as you say.  Also the cranks are different with parrallel vs the taper set up.

[pancho]

No doubt the parralel pin is important , I saw the drive side crankcase on Matt Daly's ride at Taree shattered at the startline [some time ago!]
pancho.