My ten year old front OME heavy springs were shot. They seemed fine after the engine swap; the fronts actually seemed to level out, losing the stinkbug stance.
Once I added the winch & bumper back on, though, it settled back down. Then, after greasing up the bushings and between the leaves, it starting flexing so well that the front would bottom out. On my oil pan.
I ended up having to replace the oil pan because I cracked the first one (more fixes are in store for that later).
After doing some research, it turns out that the "heavy"s (CS004) are really only good for a stock truck, or stock + a bumper. If you add a winch to a heavy bumper, you really need to get the CS005, which adds an additional leaf. I'm not sure why anyone would ever order "medium" springs up front.
So, I ordered and slapped on a set of the front 005's (still have the old rear 004s). Now it rides like a sporty caddy and doesn't bottom out anymore. And the truck finally sits level. I've got maybe 200 lbs over stock in the back right now with the bumper, tools, and some other crap in there right now.
Per the tape measure, it went up an inch in the front.
It seems like the best combo if you have F/R bumpers + a winch is the CS004RA rear springs (don't do the A/B thing) and CS005F up front.
For a totally stock truck, I would do CS004RB (B is heavy, but less arch than an A) in the rear, CS004F up front.
Either of these combos should result in the level-est stance and best ride possible.