I agree with Chris "Go for it", I did the upgrade on a number of my GPs. The best result was using the Cruise -Light. I previously had done several other conversions of the GPs using the Mini-2, which gave me the TMCC capability, but lacked the ability to build a consist and have all of the effects available such as the Rail Sounds horn and bell and the reversing headlights. The Cruise-Lite overcame all of that and fits into our S gauge diesels.
I do need to mention the lack of these capabilities on the Mini-2s is experienced using the Cab1-L Legacy.
Brendan, just make sure as you prepare to do the conversion to have an anti-static mat to work on.