Opening out the splashers was slow work using needle files.
Using a power tool struck me as potentially too uncontrollable.
And you need to be extra careful at the front; I still took a bit too much off!
My advice is to plan on minimum sideplay on the front wheels.
Then file, continuously measuring to that minimum clearance.
I warn you that I am not particularly happy with my result.
The slow-running performance is not good.
Maybe you will get better running using the Hornby brass bearings reamed out rather than running in mazak;
I missed that conversion option!