So I ordered some parts and waiting for them to arrive on my continent.
Ordered a tool to hone the rocker arms and towers to a proper ID, but the tool was wrong and could not handle such low ID.
Need to find a different (and affordable) tool for that purpose it seems.
I will need that to fine hone the aluminum spacers as well.
In the meantime I took a closer look at the camshaft chain toothed gear that mounts onto the crank.
These are different and not interchangeable. Seems the later engines with the 8 holes for flywheel used a wider chain.
The locking/positioning is also different. The older type gear uses a "tip"/hole while new type is woodruff key.
Unfortunately the "tip" on the older hear is too narrow and leaves about 1mm of play on the newer crank.
So the idea is to machine a woodruff key seat in the older gear and fix it the newer way.
The crankshaft nose length to the gear is same for both generations of the cranks, so the gear will be positioned in the same place.
Only difference is on gear width where it touches to the pulley/harmonic damper (?) the older gear is 7.2mm the new one in that place is 6.8mm.
But I guess 0.4mm would not be an issue for the pulley to be moved forward of the engine?