This drawing seems to be right on the money. So 4.9mm for the inner diameter.
I measured the bolt to 4.8mm and the inner diamter to 4.92mm. Its not super snug, but a lot better than the original wheels.
No I won't be using the original plexi parts as I ordered the small wheels to recover some travel - but it looks like the bigger wheels could fit the original plexi parts, maybe needing 4 instead of 2 eccentric spacers (unsure how much adjustment one side will get you).
Given I have 22? T-slots and only need 6 I will try a few methods for sanding/lapping, filing and milling/routing to make a V slot on my 20/20 alu, to get even better support and avoid wear over time. Unsure why there is the little step on these profiles instead of just a small chamfer which would have been a small v-slot.
First up is sandpaper on glass as my 90 chamfer mills are still in transit. But given the small amount of material to remove i think it will work well. And I think I might want to sand/lap after making a deeper V groove on the mill/router anyway.