[GlennBurnage]

Many thanks to those who have replied with most helpful advice.
I may not have made it apparent, but this car is a Werner Oswald Frazer Nash Le Mans Replica 'replica' using, almost exclusively Bristol 405 compnents.
Julian, As I suspected, it doesn't roll forward freely in 1st gear. 1st gear works fine and is quite a high ratio, so I would imagine it is standard and the non-syncro is very evident. Any thoughts about the fact that the freewheel doesn't work but the 1st gear does?? From what you mentioned in your reply I might suggest that it may have been 'modified' to over-ride/remove the freewheel?
The high ratio of the 1st gear makes me suspect that it's not an ex-AC box and I can't find anything in the car's history file that mentions anything at all about the gear box, let alone any deviation from standard or any modifications.
You mentioned that there were 'fixed' 1st gears in period - do you know anything about how, without dismantling, one might tell? I could see no alternative 'Fixed 1st' parts in the manuals, or mention of it. I have no info regarding the donor car and not sure, yet, if gearbox/overdrive has any numbering on the cases. Some time after the car was assembled (mid 80's ish) the engine was completely rebuilt, but I feel that nothing was done to the drive-train and there are a few 'whirling' noises, depending on the speed/gear/load etc, which merit investigation. I intend to have the engine/gearbox/overdrive unit out once the first salt is down.
Once again, thanks for taking the time for the detailed info and any pointers would be helpful