Hi Vocky,
Here's my progress with the balance-shaft removal. I wanted to ensure that this could be retro-fitted cheaply at a garage without taking the engine out, so I've designed it accordingly.

You firstly remove the old balance-shafts, then you insert the inner-bearing turned-plug on the end of the M8 stainless-steel studding. The shoulder stops it going in too far.
The ecentric 10mm thick M8 tapped washer is then run down the M8 studding by deflecting the M8 studding by 4mm until the washer clears the inner wall of the outer bearing casting. The outer aluminium turned plug is then inserted in the outer-bearing hole and bolted up using an M8 lock-nut and washer.
The whole thing cannot move in or out now, and is firmly located.
I'll be using the outer-bearing plug to offer a mounting for the new chain-guide.
Steve