What's your favourite mod?

I agree. The boiler shell and crew cab look quite a bit different from Gordon's. I'm still digging through the builder's blog to see if I can find more information.

EDIT: So, running his blog through MS Translator, it appears that he salvaged these trains from his then-teenaged son's childhood toy stash. He does say that 971 is a modified Gordon but there weren't a lot of details. Based on some of his other blog entries, I presume he modified it with balsa, filler putty and polystyrene sheet.