Joe - for your spacers, you only need to indicate the outside diameter, the inside diameter, and thickness. Then any machine shop (or you) can produce the spacers. You may be able to find spacers at the hardware store, or use a steel and copper washer together. The hole diameter is probably an M10 or M12 bolt I'm suspecting.
As for the remote oil filter, search the Project threads for Hanibal's build. He did this on a his bike and his work and design was top notch. (It's not copyrighted, so steal away;-)
An idea for your header mounting issue: Chris @MotoGP makes a very trick exhaust that has flanges that seal against the exhaust port, then pass thru a mounting flange. These 2 pieces are installed individually, then the pipe is slipped onto the installed flange, and secured to the flange by high strength springs. Makes removal a snap (maybe a solution for your oil filter) and easier assurance that each pipe seals against the gasket. If you need better pics for an explanation, et me know I may have some close ups to help.