I would have responded earlier. I have more engines than I can fit right now. I stopped buying them. I did sell off a couple of early models and intended to upgrade with PS3 replacements. I even gave one to a friend who I felt deserved one ( a famous OGR member).
In the beginning, I cut most of my stock 3 rail pilots and add a shim to make them fixed. I then found that I could buy fixed pilots. Only a few were available.
Later I casted my own fixed pilots. The last few models I converted, I went back to adding a shim.
I saved a few stock 3 rail pilots for any engine that I'd sell later on as a 3 rail model. My only ACe in UP paint is already equipped with fixed pilots. If I did have 3 rail pilots, they'd need to be painted to match UP colors.
Added to the fact that you only have 2 2rail middle axles, I skipped by this post. You probably need someone who has a six axle set of hi-rail and intends to make a 4 axle engine into scale wheels to trade with.
I do have a set from a GE model UP DASH8 I believe? I never looked to see if they match the ACe.