Yes oilers are legal. IKF does have a size limit though. Don’t know what it is off the top of my head. Comet kart sales or Russell’s ought to have one. For your world formula a good lube and keeping the chain clean is probably sufficient. Did either of the other w/f guys run one? Both Abbas and Letterman are good guys and I’m sure they would be happy to help you. Mike Schorn or Terry Ives are also good contacts for info on road racing w/f motors out west.
If you send me a pm I can probably hook you up with them.
And yes most of the ones the NCK guys run are home made.