Fullwidth axles were all the rage a few years ago but seem to be less so now. Most guys who drives their rigs on the street don't want hassles from the law, and most trail only rigs are showing up in competitions, where narrowly spaced cones make wide axles a liability.

I think that they make sense on something like a Samurai or flatfender with a really short wheelbase, but with the wheelbase of a Toyota stability shouldn't be that big of an issue on most trails.

Also consider that your "free" axles will likely not be so cheap once you have them installed under your truck. The passenger side spring pad is cast into the center section of the housing and must stay in the same place, but Chevys used wider spring centers than Toyotas since the frames were wider. You "could" just weld on the driver side pad in the right spot, but then the driver side of the axle would stick out 4 inches further than the passenger side. The best way to deal with this is to narrow the housing and axle shaft, which is not necessarily cheap or easy.