4 speed transmission options for a Mark IV

I have a Mark V engine and transmission in my Mark IV. I examined the transmission and found chipped gears. Since the numbers do not match, I would like to put in a 120 or perhaps a newer Jag trans with all synchromesh. What are the options?

Any trans with a JH or SH serial number will be a direct swap. These were used in Mark V, Mark VII and XK120.