Just for you Mr B, I went back out to the garage to solve the mystery! Couldn't bear you not sleeping
So up ended gearbox, put the cover on the release bearing, got it near enough center as I could and well....
Looks as though when I thought the chain tensioner was goosed and letting the chain droop causing engine to lock when rotating by hand, it was actually the cover plate hitting the casing
so when priming the engine it cut the groove, then was fine until operating the clutch obviously that must move out slightly and causes the noise.
Comparing it to the OEM cover, that bit is bigger on the blue print one, OEM one is smaller and more curvy, plus sits further forward away from the casing.
Hard to see in that picture, but it's no where near the casing.
OEM on the bottom
Don't know what to do now, either grind a bit of the casing away or grind the BP cover (risking unbalancing it) or lob the OEM one back on after cleaning it up?