I can't speak specifically for the MKT, however, as a general rule, they tend to be placed around the Lights on one side of the track somewhere. Most Roads actually have rules about how many feet they're supposed to be from or to other things (Rails, Road, or Crossing Lights themselves). However, this is the kind of information even web Foamers tend to regard in a similar fashion as Tax Law, we all know it exists but few really want to care about it (IE, good luck hunting it down from a specific road, but you never know).
Usually they'll place the box or Hut (cabin?) in some kind of place that makes sense not too far away. If theres a signal associated with the crossing sometimes the box will be some distance between the signal and the Crossing, but its rare I've seen this.
Probably the best thing you can do is hunt around on google maps for still existing Former MKT ROW on Google Maps (Or in person since you seem to live around the kind of area MKT Used to operate in?), and see how its set up there. You'd be looking for Crossing Light Poles that don't look like they've been replaced since the MKT died. I think the Katy kept up with the more modern stuff at the time of its assimilation, but /shrug. You'll probably know that better then I will. If they did theres a good chance you'll find stuff that Katy itself installed then not. If it didn't then it'll get alot more difficult.
Good Luck,
Falcus
