Interesting, never even heard of it previously even with guy's I knew 'back in the day' who raced Triumph twins with just about any mods you could think of (trying to stay 'competitive' with Suzuki/Kawasaki engined Rickman, et al framed bikes) I would think 'Y' oil-ways would be more for cylinder lube though as even a very shallow angle will not direct much to the underside of piston crown? (small end will be better lubricated from piston skirt scraping oil off cylinder walls and some will hit underneath piston.. Piston acceleration with te relatively long stroke motors would probably negate much cooling effect but I have seen many 'pretzeled' BSA/Triumph rods due to small end seizing (sen it on XS650's also)
The oil jet pointing at piston crown was actually copied from late 1920's ~ 1930's aircraft system. I'm not sure who used it first but was 'kinda' well known by time Rolls Royce designed the Kestrel . There is a lot of 'declassified' research available from NACCA, NASA , various defence ministries, etc, the 'trick' is to find whats useful and apply it to a different form of engineering (I think I may have 'invented' a new form of wind powered generator - unless Tesla did it first 100 yrs ago ;D )