What about rear wheel toe in on Omnis?

I was invited by a friend to join a group of faster cars that run up Angeles Crest Highway early on Sunday mornings. The group consisted of a Turbo Z, Turbo X19, 350 Camaro, Me, Accord, and 3 Turbo Sonnetts.

My GLHT has: stock front sway bar, Spiva rear sway bar, boxed rear axle, and poly everywhere except dogbone (got rid of vibes by tossing it). Front wheels are set up with slight toe in and all the negative camber I can get out of the camber bolts - 2 degrees I guess. Rear wheel alignment is stock - no toe in, no camber - the spindles are just bolted up flush to the spindle/axle plate. Stock 15x6 wheels with 205-50-15 Dunlop Direzzas (300 treadwear rating).

The car does not understeer. It oversteers. An autocross instructor in a "stock" Accord followed me all the way to the top where we stopped for breakfast. When we got out of the cars, he complimented me on the fact that he enjoyed watching my Omni's "perfect slip angles."

Well, that's fine once the car is "set" and the front wheels are pulling you through but it's a bit spooky on the entries when you're backing the car into corners at 60 - 90 MPH - on a mountain road.

I'd like to get a bit more understeer. I was told by one of the others to "toe in" the rears and also to put in a little neg camber too.

Sounds right to me. What does the board think?

Then, what's the best way to do it? Someone said the dealer has shims. If not, then washers? Shim stock? How thick for starters?