No goo!
The early ones are 1.5x3 or 1.6x3. The later ones are minimum 1.9x5.8, can use 2x6 (Harbor Freight O-ring kits have those) in their place. If you have the tiny ones (K0 thru early K2 Old Factory engines) on the larger oil jets, you can use either one (these normally take the 1.6x3 size) if the jets are recessed into the head like most were. If you have the early K0 sandcast or diecast K0 before about 1/70 with just the drilled hole (no oil jet) then you are stuck with the 1.5x3 as nothing else will fit the cam bearings, when the head side is flush.
When I rebuild these early heads, I use the 1.5x3 (or 1.6x3) and also a 2x7 around its outside. These fit well together and help reduce the loss that happens while the engine is cold. After the oil thins out, they don't weep anymore.
If you have a racing cam and want lots of top-end oil, you can also increase the feed-hole size (if you can figure out how to remove any chips that might fall inside the larger jets) to as much as 0.044". This leaves the strainer holes (0.0335") smaller than the feed hole without restricting anything, and the cam followers will appreciate the extra drink above 8000 RPM.
I recently rebuilt a 750K5 that was ridden from Michigan to California, then the engine pulled out and sent to me for a show-style resto (which it won!). When I got the engine from the owner and tore it down, I discovered there were NO oil jets in the head holes (empty holes!). The cam looked terrific, and the inside of the cam cover was washed shiny clean, probably form the extra oil flying around up there. The bike exhibited no problems in the whole 3000 mile Interstate-speed trip across the Rockies (except some wheel slip in the snow near Vail Pass, he said) and the bottom-end bearings were in perfect condition. We have no idea when the oil jets disappeared, but it didn't hurt anything that I could see nor measure.
