Don't do it. They sound completely different. You'd be better buying rear speakers from the current Silver range, which use similar designs to your era Golds. And it'd save you plenty of cash.
I had front speakers from the Gold range with rears from Radius & later, Apex ranges. The tweeters didn't match well at all. Personally, I much prefer the gold dome tweeters from the Radius / Silver / Apex ranges than the ribbons of the Gold range. The ribbons were thin, sibilant and dull in comparison, especially for movies. Scenes that I knew well that should have been exciting and dynamic were just 'meh'.
If you went for ribbon rears the result when effects steered from front to back would be that you'd wonder where the object has gone because in the transition it would lose its peppy zing.
Go for Silvers for the rears and keep your GS golds for the front. Sure all our tastes are different, but I think you'd be disappointed with the ribbons.