The above comments highlighted an issue which I did not know--
ie My car was originally a non-overdrive, which I changed to an overdrive version gearbox, and was installed when the body was off the car.
However the difficulty arose more recently when I needed to remove the gearbox again. With the body was back on the car, removal of the gearbox was frustrated by lack of space at the rear of the gearbox. What the comments above highlighted was that the rear floorpan on an overdrive gearbox has an additional cutaway with a access plate, which allows access to the bolts at front of the prop shaft, and more space to lift out the gearbox out.
I also found a Utube video showing the floorpan cutaway.
The gearbox now is now out. Hoping to putting it back in very soon, I wonder if Ill get away with a couple of hours work on Xmas day !!
Lesson learnt- The reason for gearbox removal was a suspected leak at the rear crankcase seal, it looked ok when the clutch was replaced. Owing to the car having been standing for number of years it only started leaking when the engine was all fired up. A time consuming mistake.
Lets hope install has no issues. Thanks again for all the comments.