Replacement starter (Powerlite RC303) now fitted and working.
The pinion engagement worked out at 8mm, without the spacer, not great but hopefully will be okay.
As for a sloppy fit, it isn't, the starter locates in the bellhousing without much if any play and with the bolts in place there is hardly any movement. Possibly helped marginally by the 2 short (1/8 long) dowels I made for the counterbored holes but I don't think they are necessary.
Now I just have to work through the rest of the electrics, first thing that does not work is the ignition warning light so I'm suspecting the 3AW is the cause.
Tony