Gearboxes XK120 interchangeable?
 

The gearbox of my XK 120 OTS from 1954 with salisbury axle (JL 21969) is damaged and I have to replace it. I found an older box (JH 3684) and I'm wondering if it will fit. I know the driveshafts have different lengths. Can I only shorten the driveshaft of the JL gearbox or are there other parts (mounting pieces?) to be modified?
Would be happy if anyone could give an advise.
Jagusch (from Germany)