The only reason the knuckle had that oil return, is because Harley stole the design from radial airplane engines of the time...which had to run horizontal and even upside down...and it was totally unnecessary for a cylinder running basically vertical...many people before this guy figured out how to run knuckheads on bottom ends that did not have that scavenge system...even (gasp) twincams.

 

pan jugs have been used on knuckles for ever cross drilling the lower spring pocket will get you a drain into a pan jug sure - one head bolt hole has to be relocated

I seen a 3 cylinder with one knuck one pan and one shovel head in jersey city in late 70s or early 80s did not hear it run as it was on the bench was told it ran

but I have done a few things in my time and a 45 engine did not return to the lower unit as its a flat head but with more money then one needs you can do anything