Hi

I have a datsun 620 I got from a friend,

The engine that's in it keeps losing compression, and with it being such an old engine, I was hoping I could find something newer that would fit?

Are there any engines I could swap into this thing without a huge amount of refabrucation?

Preferably something newer, with the upgraded obd system and maybe fuel injected if possible

Thanks for your input and am open to any suggestions for good solutions to this problem I'm having with this truck.