ES001 MSS ENGINE

After immense effort by many skilled people (and a yawning chasm in my bank balance) I have just brought a 1937 MSS back to life.
However its burning vast amounts of oil. We have traced the fault (we think) to the oil control ring being in the wrong position, However it is hard to understand the piston changes around this time.
In 1937 (?) Velocette introduced the barrel oiling system which presumably required a different piston / ring set up ?
Can anyone please tell me the different piston and ring set ups used in the 1930's for the MSS ?
I would be immensely grateful as even now the only way to reduce the smoking to an acceptable level is to cut off the oil supply to the holes in the rear of the barrel, which makes me nervous. (All breathing and top end issues have been thoroughly investigated) - Martin Hughes 21/9/2003