My feeling about it is if you're going to put a more modern motor in, want front disk brakes, AC/PS/PB, IFS and all those modern conveniences, then do the chassis swap.
Lots of dudes use longbed s-10 frames for such projects, and one outfit even makes a kit for the AD trucks.
I've seen old bowtie trucks slapped on everything from s10 frames to Oldsmobile Cutlass frames.. just depends on how good you are with a welder, and what you have available to suit your needs.
