Thanks for the replies, I appreciate it.
Good to know the sump plate will fit, no problem making new mounting points.
That Courbin seat does look comfortable, looks good too.
The 3AJ seat looks comfortable but not so stylish, bit blocky.
I had been looking at Welcome to the Frontpage
which is a couple of counties from me.
The can add 1" of foam, recover and post back the seat for around £100.
The thing is the original seat looks good where it meets the rear mudguard.
I never carry a pillion so would like to keep that part thin.
I could always buy some foam and try to cut it and shape it.