The usual Singlespeed off-road ratio-- the "standard" ratio for SS 26s-- was always a 2:1, which is about 52 gear-inches. For klunkie builds based on industrial bikes like your SHD, I think it's best too err on lower side, as they can be heavy. Of course, i'm heavy myself so, as always, YMMV.
Another consideration, if you're still trying to decide on the front ring, is clearance. You're less likely to buzzsaw a log when you're hopping/klunking/lugging over it if you have a smaller front sprocket. So, here'd be a benefit to going small in the front and then fining your 50" gear off of that. The drawback, of course, is that it won't look as cool as a 42 or 44t front sprocket. (BITD, when I first started riding SS mtbs, the typical set-ups were 32x16t. I ran that, or sometimes a 32x17t. When I rode a 29" wheeled SS, I went 32x19t to make up for the larger final drive...)
I'm currently building a bike for trails which will be set up with a 42x22, which comes out to a theoretical 49.6" gear. I'm not worried about chainwheel clearance, but then again, my frame is a 26 and has a pretty high BB...
