Any unit can fit in if you have good mechanic. I have seen modded CJs with OHC steering unit and pump and one with Fiat unit [dunno which model].
Seen ex-army MM550s with steering pump fitted on bumper in some other forum site. They were Toyota Hilux unit.
Since you are from Munnar, you can get hands from Muvattupuzha [land of Jeep mods in KL].
MM540 got Peugeot TUD-5 right???? or Some other Peugeot unit??? If it is TUD-5, then Esteem D, Zen D, Peugeot units can fit in without any issue, which can be procured from second hand market.