The suggestion given for using the later diff is only using the center section, not the whole assembly. easy swap, no setup on the gears needed. Should be able to swap it without even jacking the truck up (advantage of the full floating axle).
As far as the ratio goes, with the stock 216, the load capacity will suffer, as the engine won't pull it. That's not to say it can't still pull a decent load, just not as much as it would with the 4.56 gears that are factory.
