Sorry to be a bit late with this.
Dan, my support bearing does not contact the crankshaft at all so no worries there.
Crush washer? These are for setting up such things as pre load on taper roller bearings in mass assembly applications - I can see no use for one here.
The Centa set up does not have any axial loading at all.
Any spline drive which will not transmit the load without the retaining nut being tight will fail - no ifs or buts.
Roll smith - There is little point in assembling something with worn splines and I doubt if loctite will withstand the forces we are dealing with here, but it would be good to hear from someone with experience of this.
On the bright side, my machine did several hundred miles making the rumbling noise with no apparent damage to the crankshaft.
I will soon have some gauges ready for people to use to check their crankshaft splines for wear.
My repair solution which seems, so far, to be successful can be seen here in the image gallery. http://www.bleazey.co.uk/M3W.html#Image
I will have some of these repair inserts ready soon.