I haven't but it hasn't had much load on it either. I'm not thinking it'll need much if any.
The Dart firewall seems to have decent amount of raised geometry all around where I mounted the Clutch master. So its not a large flat area like the E & B bodies. And the Steering column retainer plate is shoring up the small flat area right next to it.
I'm not about to do any FEA on it but my experience in FEA tells me it should't be too bad,,, that and just cranking on it by hand to give it some side loading lol.