12 foot walls, 30 foot span, 1259lbs lift at full height.
Woody,
Have you considered lifting each side of the truss, from inside the barn, upside down up on the top of your walls so they are hanging upside down?
You can then move them against holding blocks at the proper location and turn them upright using a couple guys with poles or rig a rope to turn them upright using your tractor. When you get near a gable end turn the last few up so you have room for the ridge/peak to get by before nailing.
I had a 64 foot wide by 84 foot long barn with 12 foot walls built by a Mennonite contractor and that's the way they did it. The trusses have a foot wide plus soffit so were quite big but they had no problem doing it that way.
Ron