Final Drive Splines (or lack of)

Hi All,
The splines on the final drive on my 90/6 are badly worn and I'm hoping to sort this over the winter.
I'm considering getting a replacement shaft from Siebenrock, maching and pressing out the old one and putting the new on in. However I believe that some re-shimming is involved and I've no experience of this.
Can anyone on here advise if this is a difficult thing to do?
Or has anyone any other suggestions re how to sort this problem (other than selling the bike to you).
Cheers.
Fran
ps anyone selling a 34/11 final drive with meaty splines?

I can do it for you if wanted

Thanks Mikeyboy, I may take you up on that if I can't find someone more local. Cheers