Yep, that is what I think too. I had a set on my 64 Chevy in 65, and it was one of the first sets in our area, so I would think mid 60's on would be right.
Keep watching Ebay, single mags show up all the time.
In about 1975 I saw an ad in the paper that said something to the effect "Lots of mag wheels for sale." When I called them it was an old speed shop that had been closed up for years and they were cleaning out the building, so I went to see what they had. Literally the whole top floor of this shop was full of every kind of chrome and mag wheel you could imagine, and they were selling them off for something like $5-$10 each !
I probably bought 5 complete sets of wheels and for years I dragged them around the country as we moved, then I got hard up for money and sold most of them off and just kept 2 sets that I used on my Mustang and my 32 rpu. I can still see that room in my mind with all those cool wheels stacked up, if only I knew then what I know now I would have bought more of them.
the wheel is an American Racing T70 R 15X8.5 GM 4 3/4 BOLT PATTERN the gold had been painted on it,found one to match it in Cali. the guy wanted $200 for it i don't think so.....here's a link that detail's all the AR wheel's made