Overhauling an engine every 2000 hours does not change that it is a 1960s design which relies on a very rich mixture and stupidly high octane fuels to not blow itself up to make what would today be very mediocre performance figures.
Rotax has some newer designs that are fuel injected, have modern piston head designs, and sometimes have turbochargers, and those represent what a "new" aircraft engine looks like.