I think that the whole trail spares thing is over-rated. I'm not even convinced that running the trailer on the same size tires, unless the tow rig tires are small, is all that great of an idea. Big balloon tires on a small, light trailer isn't a stable recipe.
I know that runs contrary to most posts on trailers, but trailers need different considerations than do tow rigs. If you effectively control the rear axle wrap the odds of needing a spare rear diff are not very high. Far more likely to need an axle shaft, but are you really likely to leave the trailer behind? A better plan, IMO, is to convert the rear to a FF so that front & rear drop-outs are a direct swap.
As far as towing power I towed the TrailBlazer with my 60 up the coast to near Oceano and was pleasantly surprised. we were loaded down for 'Glamping' (3 cast iron Dutch Oven's + their steel table, margarita dispenser, etc.) and the whole loading + trailer only cost 2 mpg. Gaviota Pass slowed us down, but not unreasonably. I do keep in mind that the altitude, even at the top of the pass, was not very high, but we went over the top at a steady 48 mph. I am curious how the 2F would perform towing this trailer at altitude, but the odds are that the V8 will go in before I get the chance to find out.
I think that the M416/M101cdn trailers are a great starting point, but they have to nearly meet your needs from the start. If they do not then a custom trailer is called for. I've longed to build a 416/101, but I am trailer rich and have absolutely no use for such a trailer.
Teh "How to Build a Trailer, vol. II" at Northern Tool is worth the price. I do not have vol. I so I've no idea if it is or not. If you can find a copy "Trailers: How to buy and evaluate" is worth at least what vol. II is worth and probably more.