Ah ok fair dos. If I had one myself I would offer to help (I'm at Carluke) but if/until I move house in the next month that wont be possible.
I'm not 100% up on the FFR's, are all the engine electrics, lights etc running 24V?
Is it petrol or diesel at the moment?
The 2.25 starter will fit the 2.5, things like water temp switches, glow plugs etc can all be transferred so should be ok. Do you have a 12V dropper because the stop solenoid feed could be taken from there.
It would appear that with the right spacer, no alterations are needed to the chassis
http://forum.lro.com/viewtopic.php?f=24&t=57073