If, at the end of the day, what you want is an external oil filter and even more additional sump oil capacity, the simplest and most sanitary solution might be something like an original Guzzi deep sump plus a Harper's Outsider. The Guzzi deep sumps have been used on Tonti-based and other big-block Guzzis since somewhere in the mid- to late-90s, so you'll eventually find one online or at a parts supplier. The Harper's Outsider is available directly from Harpers or occasionally as a used piece. You could easily sink $3-400 bucks into obtaining these parts, so there's an economic challenge.
Since you probably don't have either of these you're considering arriving at a similar end result by using the parts you have on hand; the Guzzi sump spacer and Bub sump. To my mind, there's not going to be an easy way to achieve this and preserve some form of serviceability and assembly/disassembly ease. Still, typical Guzzi owner frugality and a long winter may yield some interesting results. Press on!
Yes. My end goal is to get an external oil filter.
Yes, I could just spend the money. I just did the MG unit on my SPIII.
Yes, I am trying to be Frugal!!
Yes, it is going to be a long winter, it's already started with the salt on the roads and not enough rain yet to was it off. Sooooo....... Ill keep plugging.