OK just went around there again this morning.

The rocker gear has been removed now and there is a quite big difference in the oiling arrangements between the W2's and the stock arrangement.

Fundamentally, on the std heads, at the top of the rocker stand is a recess around the bolt to provide oil to the shaft. This recess intersects with the oil gallery coming up through the head.

On the other hand the W2's have a VERY small (say 1-2mm) gap on the lower side of the stand (maybe 4mm wide - the bolt hole basically covers the passage for oil to the rocker shafts. Forgive my ignorance, but is this "normal" it appears to cause a massive restriction in the oil system.

I'll try and post some photo's shortly.