I added an oil filter to mine ('70 T120R). Takes the same cartridge as the Tridents did. Also have electronic ignition, mikuni carbs, solid state rectifier and voltage regulator, led tail light, halogen headlight, all while maintaining the original look. Oh and I have stainless spokes laced by Tom.

I am thinking hard about selling it though.
The sludge trap that runs through the crank was the "secondary filtration" system.