Pushrod operation. The camshaft is arranged with the lobes side-by-side, and the valves are of course one above the other. This means that the pushrods cross on their way up the side of the cylinder.
The inner lobe of the camshaft - nearest the piston - is the inlet.
The rockers run on shafts that run across the rocker box. The shafts are drilled from one end up the centre, to supply oil to the rocker bearings. Each rocker has two bushes pressed in at the ends, that run on the rocker shaft.
Both rockers have their endfloat taken-up by a spring with a shim washer on each side. Due to the thrust of the pushrods being in different directions, each rocker has the spring on a different end. The inlet rocker has the spring at the valve end, the exhaust rocker has it at the pushrod end.
The inlet rocker shaft has an arrangement to deliver oil to the stem of the inlet valve. If you look carefully at the bearing surface of the rocker shaft furthest from the threaded end, you will see a milled flat. This runs lengthwise on the shaft. It provides a small gap to allow oil through from the high-pressure area between the bushes in the centre of the rocker. The line of the milling will probably be in line with one end of the slot cut in the large end of the rocker shaft - the end without the threads. Mark the outer face of the end of the shaft or mark which end of the slot is in line with the milling.
Now take a look at the inlet rocker. On the valve end you will find a slot cut across the end face. This must line-up with the milling on the rocker shaft when assembled. This slot takes the oil fed down the milling and leads it out towards the inlet valve stem. When you reassemble the rocker box and cylinder head, turn the engine over until the inlet valve is closed. Use a large screwdriver to turn the inlet rocker shaft to line-up the milling with the slot in the end of the rocker - you should be able to see the slot with the rocker box cover off. This will ensure that there is an oil flow when the valve is closed and there is little pressure on the rocker bushes. When the valve opens, the slot will rotate away from the milling and (hopefully) the rocker bushes will enjoy full oil pressure.
The exhaust rocker shaft has the same milling, but it is not important. As all the oil from the rocker gear drains out past the exhaust valve, there is no problem with lubrication.
Take particular care when you put the rockers back together that the valve-opening fingers are properly over the ends of the valve stems. Use a torch to check, after the rockers and pushrods are assembled and the nuts at the end of the rockers spindles are pulled-up tight. You may have to play with different thicknesses of shim washers on the ends of the rockers spindles, but do take care that the springs used to allow a bit of end float do not become coil-bound. If (when) you drop a shim washer down into the pocket around the valve stem and spring, use one of those tools with a magnet on the end of a thin rod to retrieve it.
Changing the oil supply to the rockers and providing a new supply directly to the inlet valve stem is a very common modification.
You can buy an extra oil line that runs from the end of the inlet rocker shaft to the inlet valve inspection cover. One source is Moto Falcone. The part number is 1006030 and its name is Kipphebeloelleitung.