Wish I had the engineering background to explain it, but my understanding is that it has to do with the low oil percentages gas/ignition systems need to run properly. There is a lot of lubrication difference between 18% synthetic/castor in a methanol motor that runs cooler and a gas system running basically 2.5 - 3 % oil that runs a lot hotter overall.

I've just always been told a needle-ended con rod was essential, but I don't "know" the engineer-un reasons.