Ideally, for a 4x4 conversion, an original Napco axle with all the extra part that go with would be ideal. However, they are not all that common, and can get pricey. Same goes for the mid-'57-'59 factory 4x4 axles (made by Napco). Adapting a later model front drive axle can be done, just a matter of finding the right width and adapting the spring pads. Some lifting will need to be done in the rear, re-arched springs and/blocks will be fine there. If I recall it correctly, converting to 4x4 on a Task Force body truck gets a rough lift of about 5".
A body lift would have to be fabricated, I know of no company making one for that body truck. I'm not sure what you have in mind for steering/brakes/clutch, but with the stock setup, a body lift would be very difficult to pull of without some major alterations to those systems. If you're going with a later model steering column/box, and a firewall mounted master cylinder/clutch pedal (Not sure if you're running manual trans or not), then that helps. The radiator could be an issue, too, as it does mount to the frame, rather than the body like a later truck.
An option you might look into, since you're only looking for around 3", is a set of lift springs for a '73-87 K10. I have seen those adapted to the stock spring hangers of a '57 that was converted to a 4x4 (Project Early Iron, Petersens 4 Wheel & Off Road). Information on that build online are somewhat difficult to come across (it was finished in 1990), I think I still have the issue with the final summary around here. If I can find it, I'll post what I come up with as to what they used.
