Right, wrong or indifferent,, this is what I have always done and was always, in the end,, very impressed with my highly skilled abilities in creating a good outcome,,, a legend in my own mind :crackup:
I dump everything OEM in there except for the little little cap that covers the end of the spring.. That long piece that goes lon top of the OEM spring is history.. IMHO,, if you did get a set of PVC preload spacers (piece of PVC pipe about 3 inches long?) with your Progressives they are plastic to make them easy to cut to the length of preload you desire.. There is no way you will get the full 3 inches in there as preload.. Personally,, I like 3/4" of preload and have always tossed the PVC in favor of heavy wall copper pipe caps as spacers cause I like to know if I decide to beat the living daylights out of my bike in some hair brained "wonder where that snake trail in the Utah Mountains lead to" moment I aint gonna end up shredding some plastic into my fork valving..
After cleaning out the old whale/fish oil that Mom Yam uses for OEM fork oil completely and rebuilding the bushings if needed, I slip the Progressives into the collapsed forks, then add some fork fluid being careful not to fill to close to the top.. Then I lift the forks to the top and screw in the fork caps a ways to keep the fluid from gushing out while I work the forks up and down to get the new fluid into the valving.. When I am satisfied that I am feeling proper dampening of the oil I remove the caps and recollapse the forks with the springs protruding from the tops of them again.. Now I take my handy dandy fork oil leveler (its a long tube connected to a syringe (gotta LOVE those large AG Syringes), slide the tube in with the springs still inside the fork and measure 3 and 1/2 inches of distance between the top of the fork to the top of the oil and suck out oil till I get air,, both sides doing this quarentees equal oil height.. I use Bel Ray 12 weight and have always found this perfect for my first gen off road travels and canyon carving needs with 2 up, fully loaded... Now I raise the forks, make sure I have the heavier wound spring section of the spring in first, slip that little OEM end piece over the spring, put the preload copper end cap with its solid face pointing toward the fork cap (up) in and set about the task of getting the fork caps on without cross threading them,, beware the fine threads.. I have found that tieing down the back of the bike if I am working off the centerstand is handy for this as it takes some serious controlled down pressure to get the caps started..
Once buttoned up I have also found,, at least for me,, no air pressure in the forks = the best handling/ride now..
I am sure I missed something here but maybe this will help somehow..