I spent the last two days trimming and trial fitting the replacement horizontal timber under the rear window.  Late yesterday I finally had it in position, including the new left upright for the registration number box opening.  Today I finished screwing and gluing it all together and some profile sanding.  All that remains on this part of the job is some cosmetic finishing inside the bus, although that is all mostly hidden by the back seat.

The next job is to reseal the rear window and install the sill timber between the glass and the new horizontal.