Spitfire Overdrive install

["Neil Penberthy" <neil@liant.com>]

I'd like the lists collective wisdom:

I have a 1973 UK model MKIV Spitfire with the older type 3 rail 
transmission with no overdrive. I also have a single rail late type 
OD trans which I'd like to fit. My questions:

1. I bought the OD trans used and would like some idea of its 
condition before I embarl on the installation. Any tests I can do ? 
(It turns !)

2. The trans input shafts have different splines so I plan to install 
the clutch and flywheel off a late type 1500. The BL parts book lists 
different flywheel bolts on the later cars - did they just strengthen 
the bolts or did the size change ?

Any other advice?

Thanks

Neil