Someone was saying the original egines were junk; actually they were tough as hell! You they had a 7,500rpm redline, but they suffered from a horrible intake design where over 2,000rpm the center cyl's would run lean, if you had ANY little problem, or even just ran out of gas on the freeway, you'd lose #2 or #3. The dual carb'd models didn't have this problem.
mine had 270,000 MILES on it and leaned out #2, put in another piston, but the cyl was scored, so there was a lot of slap.
Eventually, the cyl wall collapsed and it wouldn't hold water or oil. I drove it for 2 weeks with NO water or oil in until it just didn't have the power to pull itself anymore.
I had a spare engine with 150,000mi on it that was stuck from sitting in the rain, I put another 75,000mi on it before I put the datsun drivetrain in it