You mentioned a spacer in the shock. That, and the rear tire size will affect how easily it tips into a turn. According to Dan Kyle, and many many others that have used it, a rear shock link also increases ease of turning. I've heard of using a shim, or spacer like you mentioned, in place of a proper link. That's different and could have a negative effect. I don't know, I've never tried it.
What size is the rear tire? Stock is 190/50-17. That tire will tip in slower than 190/55 will. But many here, including myself run the 190/55 for that very reason. Some run a 180/55, but I think you need a 5-1/2" rim for proper mounting. Our stock rims are 6"
It sounds to me like you just got all the wrong geometry going on.
I don't know your ability or knowledge, but when you say the forks are getting serviced, what exactly is being done? Just a fork oil change? They should check the service limits of the springs too, assuming they're OEM. Which are meant for a rider in in the 160-180 lb range. So obviously, when you get the bike and forks back, set your riders sag front and back, and work with your compression and rebound settings.
One last thing. It was a total? Was it wrecked, if so then there's a lot to check for straightness. fork tubes, lower and upper bridges (triple crowns), steering stem, clip-ons, frame, brake rotors, probably more I'm just not thinking of.
John, 2000 RC51 #000100