In the older days of Trainz when I played TRS2006, TS2010, and a bit of TS12, I would use the Display Custom HUD v2 rule (<kuid2:61392:1070:1> mc Display Custom HUD V2). It was a builtin rule at the time and it has a nice GUI for the grades, speeds, signal, junction directional status, and total distance. It was a nice little rule when I was driving my trains.
TS12 and TANE I would use the builtin (and still builtin according to TRS22) the Display Custom HUD (<kuid:-3:10206> Display Custom HUD) until it was fully replaced with the new TRS19 HUD. Now I use the new GUI that's shown by default.
cheers