... I had some time to elaborate on my idea....
it goes something like this...
Three locating pins for oil pump, mounting surface of oil pump, are precisely machined compared to crankshaft position. Surface for oil pan cover is same as mounting surface for oil pump... This surface and locating pins were precisely machined because oil pump has a gear etc.....
Oil pan is bolted with 10 m6 bolts. Those bolts combined can handle 14000N of force. 10.9 M6 bolts
I calculated using some simple equations for spur gears that maximum upward force on idler gear is around 5150N if engine is making 100Nm at crankshaft. All FEA simulations I've done with safety margin... at 6250N of upward force. So you are locking at maximum displacement of parts when subjected to 6250N of upward force. Displacement is magnified several hundred times in some pictures so it can be visible. When force is in downward direction deflection magnitude is the same....
There is a lot of material around the oil pan mounting surface on lower engine case and it is really nicely spread around... I haven't run FEA on lower case but I really think it can support several times more force.
The smart part is how to locate my oil pan in correlation to crankshaft position... Actually thats easy because like I said three locating pins for oil pump, oil pump surface are precisely machined in compared to crankshaft position....
So there will be a simple helping tool(precisely machined)... Simple plate with three holes for oil pump 15mm locating pins and three holes for 8mm dowel pins and several holes for m6 bolts. The goal is to drill three holes in lower case for three 8mm locating pins. The pins are the same like in cb750 head.... three 8mm holes on tool are guides to were to drill 8mm hole on lower case. Three holes are located where existing m6 holes are in lower case so it is just to expend them to a depth of 6mm. One would need 8mm H7 drill, I can provide. Rest of threads in this three holes will be undamaged and used to bolt pan... You can see the tool in last picture
Oil pan is modeled in the way that it is 2D job for CNC(cheap). Oil pan is AL 6082 T6...
Idler sprocket holder is made from 4320 steel. There is no space because of crankshaft etc... for aluminum version
Oil pan and sprocket holder are connected with four m10 bolts... and two locating pins. I will add also adjusting layer of thin measuring steel between pan and sprocket holder.... so one can adjust height of idler... just in case....
Oil pan will have a slot for 1.5mm rubber ring on upper edge to seal with crankcase.... Also oil pan should not interfere with exhaust
this is not final and suggestions are welcomed
..... and maybe I am wrong and this is not possible