greeting and help please!!

Greetings all! a big hello from sunny Gloucestershire, how are we all today??

It was only by chance i discovered this site which brings me to my reason for being here.

I've got an early series 3, rusting and twice as old as me but its still the best thing i've ever owned, far more enjoyable than any car i've ever owned!

Problem is this:

It has been fitted with a Rover SD1 2.4 TD engine and attached LT77 gearbox, the box has been very much adapted and has stripped the rear mainshaft splines where it drives the drop gears in the transfer box via a conversion piece of unknown origin.... not good.
Now i'm no mechanic, but I want to do anywork i can myself, learn a bit and save the pennys going down the drain.
What i was looking for when i came across this site was anyone else who might have the same conversion as on my series or anyone who has a workshop manual for an lt77 so that i can split it and replace the mainshaft.

I would replace the gearbox but its been so modified, it would be horrendous to even consider it, the rest of the box is fine the gears all function normally just the rear mainshaft slips under power now and is verry loose. I have considered a keyway or similar idea but have been told that it wouldn't last too long.

Ideally i would like to A- replace the mainshaft and B replace the outer splines on the conversion


If anyone can help it would be very much appreciated.

thanks

Ade [email protected] (my bands website before you ask