I had challenging moments like yours. The 68 XLCH has three fittings on top of the crankcase a little back from the rear cylinder base nut. I've included a photo which should help.
As you progress, if you are fitting the "lunchbox" oil tank used from 66-70 the oil feed out is at the bottom, the return line is about 3/4 up the rear of the tank and the vent is at the top.
The XLH from 67 on is very different and has it's feed line to the back of the oil pump and the vent line comes out of the back of the cam cover returning to the tank and the return line on the top of the right hand case. This is because of the placement of the electric starter.
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