Difference between Mahindra Jeeps -
MM540 : It came in both 2WD and 4WD. It had a 2.1 Litre 62 BHP indirect-injection diesel engine (XDP 4.90) with a 4 speed Gear box.
MM550 : An MM540 itself, but with 4x4 (no 4x2 variant) with refreshed interior and a 2.5 Litre 72.5 BHP indirect-injection diesel engine (XD3P) with a 5 speed gear box.
MM440 : MM540 fitted with a petrol engine (hurricane F-134). Only in 4x4. Later it also had a 1.8 litre Isuzu engine and was called MM ISZ.
CJ340 : The civilian jeep (CJ) was produced in USA. It had different versions over years like CJ3B/2A/4/5 and so on. In india, Mahindra manufactured the CJ3B. It came with the Peugeot 2.1 engine. It had a SWB (Short Wheel Base) chassis.
CL340 : After 1970s, CJ was renamed as CL.
Classic : It was a limited edition CL340.
MM650 : It was the MM540 with LWB (long wheelbase chassis). Was also available with 4x4.
MM750 : This was a longer MM650, targeted as a UV to transport people.
None of these are available today. you will have to buy an old Jeep and restore it.
Alternatively, you can buy the Thar Di or Thar CRDe.