Sounds like you've got good brakes at least. The driver's depth perception may be questionable, but the tractor's brakes work...
Seriously, you don't even want to brush up against a tree on the outside of the wheel. First off it's not good for the tree, and second off you stand a better than average chance of wiping out the valve stem on the tire, leaving you with a flat. But, if the tree is ending up on the INSIDE of the wheel, you weren't brushing up against it on the OUTSIDE... Just stay away from the trees, and if it's too tight to get through where you need to go on a regular basis, do some trail building. Get rid of the trees you have to rub up against to get through.
"Safety valve?" What's that? Remember, it's 1954.
As far as towing your tractor, see my response above. Take it slow and use common sense. Your "panic move" should be lowering the 3pt to put the wheel-less front end of the 8N on the ground, turning it into a boat anchor.