Greetings from Mancuria my Salopian friend. I was resident in the metropolis of Hadley .([Telford]
Re grey import bike, No oil cooler so could be jap import , OR could be a normal model with GT engine fitted!
( I have 2 so

)
Firstly need to establish if jap import , easiest,look at tyre info on rear mudguard inside by tool tray * actually on the tailpiece I noticed to night*if still there ....if jap writing ...import, Now you are in for an interesting journey , The frame is 1/2 " shorter than the normal model so a 650 seat won't fit, a 550 one will fit but leave a small gap around the tank.
The best option is to get yours recovered , it'll solve a lot of hassle, too many people advertise seat will fit both , all etc..
Coupled with a seat from a UK model is 30 odd winters old the front will be rusted unless it is a gulliari aftermarket seat or base in fibreglass.
Search Highlander ...Kevin Jones he has done 650 seats in the best match and knows the shaping.
May still have some material left. He can emboss the katana logo in aswell if required . Not too far from you.
Kevinhighlander@yahoo.co.uk.