two years back i replaced a friend's Jimny (potohar shape) 660cc engine with a potohar engine.The cost was about 50000 and it was a total flop.The potohar engine used to run on very high revs and it was impossible to run the jeep over 70/80 kmph. We eventually had to get the engine overhauled.Even that did not solve the problem and had to get rid of the jeep.
I would sujjest you to get an origunal jimny engine 660cc as it matches the rear differential of the jeep and is very cheap compared to the potohar engine. I was offered one in good condition in 20000 here in karachi at that time.