I wonder if it may be the vacuum pump?

Since this is a conversion, I can't help much....but having the oil gauge under the hood, I have to wonder if there is a working temp gauge.....synthetic leaks out a lot more then dino and does burn off a lot easier....plus your using a thin oil....not being able to monitor the oil pressure during drive, I wonder if it went low....I am also not positive about the drive line, it is possible it isn't correct and it put more strain on the engine....

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