I haven't done it with a 55 2nd onto a 99-up but I did do it with a 47-55 1st onto a 73-87 GM 4x4 frame. I had a 1979 K10 that had some serious rot issues but had a 4 speed, cast iron transfer case, Dana 44 front axle and I swapped in a GM Corporate 14 bolt. It had power steering, power brakes with front disc/rear drum but there are conversions using mostly off the shelf GM parts. The only thing custom is the $60 caliper brackets! I had a rough 1947 cab and the floor was swiss-cheesed. I rebuilt it with sheet metal and some angle iron, moved the cab mounts and used the later model steering column. I think the hardest part of the whole thing besides having to engineer a floor was to get the cab to sit where I wanted it- having the front wheel opening in the right place and getting the steering column where I wanted it. I also made triangulated brackets to put the power brake booster on the firewall and used one out of a camaro so it fit in on the smaller firewall. I never did get to finish the project and had to sell it off when I hurt myself at work, lost my second job and had to move with a months notice.
I know the newer frames are a little wider so keep this in mind when you are going to be making your frame mounts and modifying your current cab floor mounts if you choose to go that route. If you wanted to make it more conventional there are companies that make frame mount kits to mount the cab and bed onto an S10 frame. I think that seems to be the way to go for a driver but I wanted something a little more rugged, truck-like if you will- complete with 8 lug wheel conversion.
http://www.ad-engineering.com/
here is a link to their website with the kits listed. They tell you which axle bolts in and fits better and which wheelbase/cab configuration frames are best for what you want to build.