I have “inherited” a spare gearbox amonst a lot of other spares when I bought my 105E. Without opening it up is there any way of telling if it is a 1200 box
stick it in 1st gear. Mark the input shaft with tippex and the output shaft.
turn the input shaft one complete revolution counting how many times the output shaft turns.
4.1 revs it is a 997
3.5 revs it is a 1200/1500
1200 gearboxes are about 2 or 3 inches longer than a 997 but as I cant remember exactly how long a 997one is to start with, this is the best method. Oh and the above applies to three rail boxes only.