I haven't done this particular swap, but I've done a bunch of similar projects. I may not do it exactly like others, but here's the way I'd approach it to build in the lowness and attitude of the body without having to fosdick with the suspension later.

If your 98 has been hit hard and tweaked, I'd find a 98 that hasn't been hit and make arrangements to rent it, borrow it from the owner or whatever. Take it to a drive-on hoist that will keep all the suspension loaded (I use the muffler shop around the corner from my garage) and measure the dimensions and angles of all the suspension front and rear and record them on paper. You'll want to use a good digital angle finder on the front and rear control arms to find the angle of the arms at ride height. Now find a public scale and weigh the car front only, rear only and total weight with 2 people aboard and record the amount of fuel in the tank.

Back at your shop, remove the front and rear subframes and with them blocked up and flat and level and using fixtures to replace the springs, set the control arms at the same attitude that you recorded on the hoist.

Make a vertical mark on the outside of the truck body at the sill, same on both sides and measure carefully from the line to the center of the hub on the front and to the center of the axle on the rear. You'll want these dimensions to nail the wheelbase when you weld in the Camaro subframes front and rear and get it equal on both sides of the truck. Remove the bed and all sheetmetal forward of the firewall and chop the front and rear sections of the frame off, leaving the cab bolted to the mid-section of frame. Install new body/frame mounts and mock up the body/frame on a flat and level surface. This is where you set the ride height and attitude of the body, like I said earlier, so you don't have to fosdick around with the suspension members to get it where you want it later. Grafting the front and rear clips to the truck frame stubs with the Camaro suspension at stock ride height will give you the proper suspension and steering geometry that was designed into the Camaro at the factory.

You'll have to rig up front sheet metal and bed mounting points from the Camaro sub frames, but if you have the balls to do this in the first place, that shouldn't be any big deal.

Once on the ground, weigh the truck front only, rear only like you did with the Camaro and make adjustments to spring rates to get it right according to the angles you recorded on the hoist.

These guys can furnish any spring in any rate for any car/truck....
http://www.eatonsprings.com/