Richard is right and you can see it in the V8 owners forum.
It helped me, because it was impossible to find a LT77 box here in Germany, it's always linked to SD1 Rovers.
With this thread I saw, that TR7 5speed is also a LT (but has different code, it's C or CL...).
Looking for TR7 gearbox, I found one very quickly, because here the meaning of LT77 is not that known.
Found my gearbox in good condition for GBP 150,00, but then you must look for a bellhousing.
Luckily found one some days before from a TVR350 for 15,00 (but with a cut-in inspection opening...).
If your SD box from 2.3/2.6 looks ok, take it !!!
If it's, beside the bellhousing fact a complete box (remote, gearstick etc), you will be a lucky man.