I frequently need to mill on the ends of long (or tall?) work pieces fixtured vertically to the front of my Shapeoko Pro. My previous SO3 model had much more Y travel beyond the bed and I need to have that back. So I milled a spacer from 1/2" 6061 fixture plate stock (pre ground parallel) from McMaster (part# 2567N31) and picked up a couple M5x60mm and M6x60mm in order to mount it.
I’ve only just started a production run now on some HDPE parts for a customer but so far so good. I’m running single flute 1/4" end mill, ramping to 0.25 DOC at 200ipm and I’m seeing the exact same surface finishes and machine behaviour as I had pre-install. Again still early to say for sure on performance but I don’t typically machine metals so I’m reasonably optimistic.