Coilover's on a fullsize.

I am gathering parts to start my SAS on my 92 chevy stepside, and up until this point I had planned to run leaf springs up front. The guy doing the work for me (because I am in IRAQ, not because I can't do it!) has suggested that going 3-link is not going to cost that much more and the benefit's will far out weigh running leafs..
Well if I go 3-link, I want to go coilover's. Neither of us know anything about coilovers, so I need to find a starting point.
What size should I be looking for to support/ and hold up the front of my truck? I plan to buy them used, So I am just looking for suggestions and what works better with fullsize rigs.

I started to post this in the chevy section, but thought I might get less flaming in here.