Here I drilled and tapped for the external return line fittings on the lower case. The other end of the lines starts at the heads; instead of returning the oil from the heads to the case through a passage in the cylinder wall, it will now return via oil lines which will allow the oil to remain 20-30* cooler than the OEM set up.
Hole started with a center punch, about to pilot drilled:
Holes drilled with a letter "R" bit:
1/8" 27TPI tap: