Not that bad...
Need to fit 90" spring seats to the rear axle (bolt on).. and then it'll fit.
110's have a larger diameter rear spring compared to a 90".
The more difficult part is the propshaft.  Salisbury axles were never fitted to 90's so you can't get a propshaft off the shelf...  but easy enough to get one modified.
The Salisbury is much stronger than a standard 90 axle, but does hang a bit lower.  Is it a disc braked one, or drum braked???
If disc, they fetch decent money, so you could sell it on, and get a very good 90 (or Disco or RR) one instead - means everythings standard.
What engine and box are you fitting??
I may have a suitable propshaft!!!  
 
 Do you need any other bits??? - plug for my add in the for sale section  
 
 Ian