Am reminded from that pic you have a huge plus on your side already - gravity. Those logs on that hillside mean you can mill downhill letting gravity do the work. Your only challenge to this at all is assembling a nicely leveled long first cut guide. Mill a 3-4" deep first cut to level it. Then maybe do a 6" deep slab for whatever 6x beams you can get from that, those cuts easily manageable with a 36" bar. At that point I'd probably freehand vertically mill the excess off the butt ends so it was closer to the width of the tapered ends. Then use a Haddon Lumbermaker or knockoff on some long straight 2x4's screwed as far out on the edge as you can to vertically mill the edges off nice and straight. You should end up with 24-34" cants depending on the log, so a 42" bar could do the whole job as Sean said. Normally lumbermakers are a PITA to use as you're pulling the saw toward you, unless you use the Granberg edging mill you can push, but on a steep slope a cheap lumbermaker device would be pretty easy to use.
