Stronger box's that will fit are any IB5 (mk5 escort, Ka, Puma, etc..) with the starter in the right place (some have them at the rear) and that run a cable clutch (some are hydraulic).
If you want longer gears then yes a diesel box will of course work.
The BC gearbox's (mk3, mk4 escorts and fiestas, orions of the same year) are all as weak as each other, including the magical diesel box that everyone seems to thing is stronger!
lol