Sorry that nobody answered quick enough to suit you,,,
The serial number you provided doesn't jive with my list that states Lister D production started in 1926 with serial number 80000?
Stationary Engine Parts in England would be the first place I would check for a bearings or other parts but I am in the states. There is very likely other sources of parts that I don't know about.
Removing the Gibb key,
I am not really a "Do a search" type of person but two finger typing large replies on a phone isn't my idea off fun either. There are many artickes and posts on the web available to you by typing in a search. All in all if there is no pressing need to remove the key and flywheel it is best to leave it alone and work around it.