Ok so this has probably been done to death, but there are always a few twists.
It’s probably ok to cut a part if you wouldn’t sell your bike before hell freezes over, or if you have a spare part you can modify at no loss. There are probably enough broken XB9s for the latter. I just like to have a choice.
As it happens the spare 9SX tail l have is from an early model. Later XBs like mine have 2 extra ribs moulded under the seat compartment, but l can’t see why unless ‘Shallow Hall’ tried to spread his partner over the rear of the seat, or in some markets they tried to ferry small children on the cheese grater and one broke!
The smooth undertray is also helpful in other ways as will become clear.
The earlier XB tails also have a different number plate lamp with captive leads. This can be an issue as the later light does not fit easily unless you ream out the hole in the casting for the later push in bulb holder. The early lamp also has a metal reflector inside which will fit inside the later unit.
I also think that black is the best colour for a cut down fender. Or if yours is silver l would paint the areas of casting under the seat rail matt black to make them less visible. I have masked off the gloss black upper seat rail to do this and to protect the existing enamel while working.
The main feature l want to include is the re-use of the end casting number plate mounting. At the rear end of the casting behind the cheese grater is a flat area of around 6 sq inches. If this flat is retained with the plate and lamp holder it can be used as the mounting point to the seat under tray. The difference in angle of the under tray automatically gives the increased rake needed for the number plate. I will use two bolts for this with 3/4 tap washers between the bolted sections to provide some flex and isolation.
It was when l came to fitting a number plate lamp that the early and later units became an issue. The later curved lamp housing is better suited to fitting in the space under the seat tray, but it won’t quite fit into the earlier casting.
l made my own mini lens unit out of a Muck Off visor clean bottle top and part of an old clear cassette case, but this was only 1/8 the volume of the original and gets too hot from the bulb. Shame as it looks neat. This would have been glued to the back plate of my 06 lamp housing just covering the bulb with a few mm to spare. I could just use the standard lamp, but l want a smaller discreet bulb cover. Working on lens Mk II now.