I bored the hole out and put the seal in yesterday. Rear cover is back on and engine ready to go back in.
Engine ready to go back in. Went back quite quickly once you manage to sort the drive shaft out and stop it moving back and forth! New silencers fitted (my mate can have his Norton ones back!). Just need to adjust the rear brake and gear lever for clearance now.
The silencers are cheap and cheerful ones off Ebay and the down pipes were fabricated for me by a friend.