Drags sell a Tee kit which you could use to put the extra tee in. Without the joint which I thought was standard but obviously isn't as you oil pipe looks original, it should be easy enough to solder the extra Tee in. If you use a 1/8" BSP joint then to connect to your oil gauge pipe, you can always blank it off by putting a 1/4" ball bearing between the (male) outlet and a spare (female) nut. I carry this as a spare in the toolbox of the KH in case I fall off.
I too am a little cautious about feeding the rockers on a MK II from the return line. This is because the oil has to go into the first rocker assembly then up and over through the upsidedown U pipe to the second rocker assembly. It would be all too easy for the second rocker assembly to be starved of oil.
My KH has the rockers fed from the return but I have added a minor restrictor in the return to the oil tank. This is no more than a bit of double diameter brass rod with a bit of bowden cable outer steel winding on the end stuffed down the exit from the return oil pipe into the (1954) oil tank. These tanks have the return pipe welded to the underside of a flat plate rather than using the hole out of the side of the return oil pipe more commonly seen. Room to get the double diameter rod into the return oil pipe is limited but the did not prevent the returning oil from blasting the rod straight back out again until I fitted the bit of bowden cable outer (less its plastic cover, of course). You might fashion something equivalent for the "hole in the side of the return pipe" system - possibly a suitable diameter spring clip partially covering the hole. Return restrictor idea courtesy of Richard Thomasson.
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.