What parts are needed to get rid of the lash+play at the *front end of the prop? Mine is paticularly rattly.

When mine did that, it was closely followed by failure. On mine the splines ended up rounding an eventually wore through. Whip the prop off and check the splines. If they are worn, itll be new prop time.

It should be locked up solid against the engine through the clutch. The only part that should have free play is the clutch on the clutch shaft. The prop clamp must be rock solid.

Are the clutch take-up springs all intact?

There should be zero lash. Rattles are normally caused by knackered output shaft bearings at the front (which are rubber mounted, I've not managed to find a supplier so far)

output shaft bearing.... pretty sure that's causing the rattle+lash: circular motion of prop(front) is not circular, has up-down/left-right rattling.

*prop's ability to move off center feels like lash to me, it baulks in gear and you hear the knocks as the prop/bearing/etc bashes around.

There is a pair of them. Standard bearings mounted in a rubber case that's moulded to the outside. I've been told that the rubber casing is an industry standard, but no one can find me a reference.

If you can suss out the shore rating of the rubberlike substance then casting your own around a new bearing would be a sexy approach.

I'll do it in course, sounds easy. There's a dozen engineering shops round here.