I converted a Legacy Mogul to a 2-6-2, and added a few pilots to some old, old, 0-4-0s. You can do this to just about any loco if you have patience and time
I looked at adding front pilots and to the RTR set 0-8-0s. Its clearly doable, but would be a bit of work, and leave me with a nice but starter-level loco - not worth the payback to me right now. I have only one Legacy 0-8-0 and would like to keep it as is - its a really nice loco like that.