[dsraven]

well, that works. nice to have a front end loader and some room.
there is more than enough info on here to guide you through the S10 swap for sure. I bet you have read through them a many times. joedoh has done lots of S10 swaps so if you have a detail to work out I'm sure he would talk you through it. skymangs as well.
it's kinda nice that the truck is a longbox so you can get the front sheet metal installed and then figure out your rear axle centerline on the fenders, then cut the front of the box to fit that space left over. maybe do yourself a favor and grab the dimension between the box and the cab as well as the height of the box in relation to the cab so you can get it looking proper when you build the box mounts. the box running boards/steps shouldn't be too hard to make work either, as long as you have some fab skills and a plan for what it should look like.
at the end of the day remember it's your build so do it how you want it, inside the legal and safety parameters.
a few pointers from a guy who did a stock 54
use a cab lift under the door openings, like several threads show with pics, so you don't bend something that will cause you more work. I use some 2x6's that are longer than the cab is wide and with a stopper on each end so the cab can't slip off one end if it moves. most guys use an engine lift under that but you could also use the front end loader
use something like the cab lift to lift the box off as well. straps from all 4 corners that come together in the middle tend to try and make each corner bend towards the middle so if there is a weak spot the box can fold in