It was an ominous time to expand the S&P pit just months before the Crash of '87 and history repeated itself in expanding the NASDAQ 100 futures pit in early 2000 as the technology bubble peaked. While I don't have the exact date of the NASDAQ expansion, my recollection from standing below it daily while at an order desk is that it happened in very early 2000. Before expansion, in late 1999/early 2000 the NASDAQ pit often had a line of 3-8 traders who stood outside and waited until space opened up so they could fit in. A good friend used to trade small in the NASDAQ pit and he complained that since he could only get a spot at the bottom of the pit, any trade he could get from a broker at the top of the pit was always crap. Yet, he'd joke that he'd stand in line waiting to be the guy at the bottom of the pit getting crappy trades.
Here's a photo also from 1987 w/the S&P trading pit covered again. A few times in 1999, I kicked around after the close at the paper scraps for anything which might be insightful into how people traded it but the only thing that comes to mind was point and figure charts because I had an old boss who joked of that method as "caveman stuff" since it was so old. Generally it appeared to me that beyond a few basic momentum indicators and the cash market, it was mostly order flow trading. To this day I'm still amazed people can trade spoos well as it's a completely different market structure than I've traded.