There's a good article in an MXA from around the time. I can dig it out and scan it if you need more info.
Basically the AMA's idea was that allowing a privateer to claim a works bike would stop the factories building unobtanium bikes and level the playing field somewhat. There were set prices (way above what a stocker would have been selling for at the time) for bikes in each class 125, 250, and Open, and you could claim, I think, one of the top three placing bikes in a race. You had to make your claim within a set time from the finish of the race, 30 minutes?
You and any other claimant would then put your bank cheque into a hat and one would be drawn out. The factory team managers tried to get around this by carrying around their own wad of bank cheques, and if a privateer claimed a particular bike, every other team would throw a cheque in the hat to lessen the chance of a privateer winning the ballot. The understanding between the teams being that they would obviously not take an opposition's works bike, they'd just hand it back.
The problem was when a privateer actually won a works bike, all the factory teams threatened to withdraw from the series and the AMA basically put the whole idea on hold indefinately. Never to be seen again
I think the idea had merit back in the day when technology was changing so fast, probably less so now when there's so much you can do suspension-tuning wise to a stock bike, and they're so good out of the box.