Lets post up some curb weights!

[Longhorn Man]

I'm thinking the coil set up would weigh more... those trailing arms are long, however, I would brefer the coils on tre track.
I would NOT recomend drilling the frame as Pontiac did...even if this is to be a race only piece. The cars had a one piece body. Firewall to tail lights...and once the fenders were bolted on... bumper to bumper, one piece. The truck, obviously is not one piece, and if you were to drill the frame, it would end up folding right between the cab and bed.
The step sides should be lighter than the fleet...simply becouse it is single wall and smaller. You could make the floor of the bed from thick plastic...plexiglass even. The aformentioned bumper removel would look kinda chopped up, but you could do lightweight roll pans to make it look better.
Window regulators could be removed and LEXAN windows installed all around.
Diamond plate was mentioned... not a good idea onless you went with alluminum. The steel stuff is very heavy.
Drum brakes are way lighter, and there is plenty of room on the big end of the track, just make sure your drums and shoes are in good shape.
Planty of places to cut corners.