Hi Pete. Once more it is decision time. To state the obvious and for the benefit of those to whom it is a mystery, this is how the oil system is supposed to work. These engines have what is known as a "dry sump". The oil pump can be considered as two pumps, side by side. Any oil that collects in the crankcase is returned to the oil tank by the scavenge side of the oil pump, which has a larger pumping capacity than the feed side.
Oil from the tank is drawn by gravity and suction into the feed side of the pump, which then forces the oil under pressure through a spring loaded non return ball valve, and then to the back of the timing bush. The bush sits tightly in a nice smooth housing machined in the crankcase, which in an ideal world is perfectly in line with the drive side bearing in its housing. The back of the bush has an annular oilway and oil holes to feed oil to the bush bearing surface and also by a miracle of hydraulic dynamics, feed oil into the crankshaft oilways and then to the big ends. The bush oilway connects via another drilling to the pressure relief valve. Depending on the model year, this surplus oil pressure vents to the oil pump cavity on early models, or as in your later version, passes to the camshaft trough via internal oilways in the timing side crankcase.
Now we come to the tragic bit. If the non return valve leaks when the bike is parked up, oil will pass through the pump, through the oilways and timing bush and accumulate in the sump. This termed "wet sumping", and is dependent to a degree on the bearing clearance and the wear in the pump and bush, and the inability of the valve to seal against gravity flow. This is of no real consequence on a machine in regular daily use, but manifests itself frequently on bikes parked up for longer periods. Here a sump plate with a convenient drain plug is a good idea. There are various options to deal with this phenomenon.
Now to consider your findings. In a conversion such as yours, you should find a non standard oilway somewhere that has been machined or plumbed into the housing to connect to the relief valve. Without removing the bearing outer to check, there should be a free flowing connection between the hole with the valve in it, (Oil pump pressure output.... push a matchsick into the hole, you should feel a spring loaded ball) and the oilway at the back of the relief valve location. Even if this has been done you can still go back to standard. If it has not been done, then you have to decide whether to go down the conversion route completely, or stick to standard. No new oilway anywhere would indicate either a poor knowledge of the engineering considerations, or a failure to complete the conversion.
Without this oilway, the oil has reached a dead end, and you have no way for oil to reach the relief valve or any subsequent arrangement to feed the crank oilways. So this is the deal breaker.....oilway in place? Stick with the conversion.. No new oilway? The bearing will have to come out either to machine an oilway or go back to standard.
Chaterlea John has given us some excellent views of what in involved. You need to find out how far the conversion has been completed, as you are already a good way there. The bearing design cannot hold oil pressure, meaning the crank oilways must be fed in a different way, the most obvious is from the end, hence the various designs to achieve this. The roller bearing may or may not have its own oil feed, but as oil will accumulate in the oil pump cavity, there is probably enough there to allow it to survive.
If you stick to standard, remember over time the crankcase location for the bush may not be round, it may be also be gouged and abused. Any leakage between the housing and the outside of the bush will result in loss of some oil pressure to the bearings. This location can be bored out if necessary, and an oversized O.D bush obtained. Also, for the best result, after installation the bush should be line bored (in line with the drive side bearing location) to give the final running clearance. If you are lucky and the case is OK, choose a one piece bronze bush of smaller size than your crank, to allow for final line boring to size. If the crank is worn or scored, just get it ground just enough to clean up the journal. Then choose your bush. Remove material from a relatively cheap bush rather than a rare expensive crank.
SRM are the experts here if you stick with the conversion and are a good starting point for more information. A fair amount has already been invested in this motor, and removing and reinstalling the roller bearing may not be easy, so think of your options and cost/benefit considerations. Done properly the conversion will give a long lived reliable engine. If SRM did the original conversion they should have a record.
Hoping this helps, and will assist you in your next move.
Swarfy.