The port in your picture that you route to the redrive is where I seem to have a factory installed plug.  Was yours this way?  If so how did you remove it, and did you have to tap it and for what size?

That gallery is plugged with a brass plug. It is part of the oil path from the rear iron through the upper dowel gallery then outboard, then down, then inboard to the front main bearing.

 

It can be drilled out and tapped for 1/8 pipe. Overtightening pipe threads (tapered) will break out the cast iron around the hole and ruin the casting. Tapping into the aluminum block on the filter adaptor pad (Rear iron) is fool proof and looks good. I would preferr not to screw with the main oil galleries if I don't have to.

 

When you have to do things like this, drill out the plug, with the iron clamped to a drill press table, and the table turned to 90 degrees. A level along the bellhousing surface to assure a square hole. Drill a perfect hole, removing 95% of the brass plug. Scrape a groove in whats left down to the iron and fail whats left of the brass with a pick. Drill the hole oversize for the  boss fitting threads. Plane the top of the hole flat with an end mill bit. The threads for the boss fitting are straight, not tapered and will not over-stress the walls of the hole. The washer on the boss fitting will seal against the end milled surface. The fittings are called "Tube to Boss"

 

Lynn E. Hanover