While not exclusively in depth, I've included generic rules for stagecoaches, wagons, etc. in Shoot N' Skedaddle.
Also added some rules for attacking trains (which are moving) in a small add-on. I don't think either are as indepth as you're looking for, but they are covered.
If you want really indepth stuff, it may be worth taking your favourite rule set and designing a specific scenario around a stagecoach chase, etc. The problem I have is that you can shoot horses in SnS, so the easiest way to cock up an escape if shoot the horses (which then require actions to unhook them from the rigs, etc.). A savvy player will just smoke the horses

(unless they need to get the stagecoach off the table, which then requires more work)