Marine,
I did one side at a time, I would jack up one side on a wheeled (floor) hydraulic jack just enough to do the job. But there is a lot more to this than you think.
I couldn't get the new bushing to fit....my cab had rotated some degrees counterclockwise over time! So I left in one rear bolt (to keep most alignment), blocked up that side, then jacked up the other side. My dad used a large "C" welding clamp to rotate the cab over (clamping against a cab-frame support).
My original 1/8 inch shims were crap (I had one on each of the four frame mounts) so I had a local machine shop make me new ones. I used the kit from Classic Heartbeat. The owner will take the time to answer your questions on how to tighten.
The original rear bolts go into a cage nut from underneath, they have pointy ends to get into that free-floating nut. The new rear bolts are not pointy, you'll have to turn those on a grinding wheel to points.
To decrease the risk of broken bolts, I used a break-free spray on each nut for weeks! I used ZEP 45 but any breakfree should work.
Now comes the bad news. You cannot replace one set without replacing the other. You have 2 more bushings under the radiator core support. You have to replace those too or your lines will never line up again. So that means removing the entire front end!
The holes in the fenders are oversized, you'll have enough play to get your door-to-fender gaps right, or as right as you can. The fenders came off the assembly line without straight rear lines! It didn't matter to GM back then.
Now you know why I don't have my truck together yet.
The good news is it will be so much easier to work on your engine with all that off. You'll have body rust there too, now is the time to fix that. We will walk you through this.
*You probably know this but it's too expensive to learn the hard way. Put a nut on the new rear bolt, then turn it to a point. Unscrew the nut to chase (straighten) those threads.