Having done many of these conversions, including 2 WBB Ten-Wheelers (so low-geared you can do without cruise control), and a Wms 027 Hudson, let me interject something:
1 - the tether on most steamers already exists, so there is really nothing to "deal with" for
basic functions. (Headlight, smoke unit and front remote coupler control, if desired, will indeed require a more-than-4-wire tether, if the electronics are placed in the tender, which is almost universal).
2 - the WBB 027 Hudson has no tether at all.
3 - the WBB 4-6-0 (and WBB 027 Hudson, I believe) has a wonderful plastic tender, which means that the antenna installation is just as simple as that on a plastic-bodied diesel - no shell/frame isolation issues.
4 - which brings us to the metal-bodied GG-1; the body must be isolated from the frame
for the antenna to work. Not hard, but it must be done. Usually simple; sometimes maddening.
5 - I usually use the speaker that came in the loco, if any. Just leave it where it is,
if possible, and plug it into the new board. I've never noticed much difference, if any, in the sound.
6 - in any case, tackle it; it gets easier. After a while, you can throw a plain DC Commander without sound in a simple diesel (WBB; early MTH/Weaver/Lionel) in 45 minutes for 60 bucks. (This could apply to the WBB 4-6-0, also)