Like CJ I considered the weld to be the feed to the timing cover, but as they don't make drills that go round corners how is the oilway formed? A brass or copper tube in there somewhere? The weld does not look like a true fusion weld, more like a lump of something sitting on the parent casting, Lumiweld or similar?
Is it a trick of the light but those three retaining bolts for the race don't look the same, so maybe not a true professional conversion. Most examples used an expensive timing side bearing which combined ball and roller elements, rather than a ball race on the drive side as here. All point more to a homespun solution than a true precision job.
The man with some of the answers is Forum member MrShifta, he has a bike which featured in Classic Bike all those years ago when end fed cranks first made the big time.
I have seen bikes where the feed is external, via narrow bore tube and compression fittings. Ugly, functional but easy to check oil pressure and supply.
Swarfy