I see what you mean!
I have just measured my old uprights and center of hub to center of caliper mounting holes is 85mm! My new uprights are nearer 100mm!
With regard to cutting lugs and re-welding I'm not sure its possible as the middle of the caliper at the moment is only a few mm from the upright! If this makes sense?
Given the tooling that marlin has I pysically can't understand why they did not just design them to take 260mm rover calipers and 260mm rover discs??
I will know more when I get the bearings and hubs in place! Hopefully tomorrow night