Yep.
And SVRA and many of the other vintage have the same one-carb rule for 1500 Midgets.
Most of us just follow the SCCA GCR as regards rules. Keeps things easy.
EMRA will allow you to adapt any single carb however, as long as you use the original intake manifold. I'm using an S&S Super G (2-1/16 smoothbore with almost no venturi.....intended for racing Harleys). It's a honking carb for this application, but I'd run the SU at first, especially if you're planning on putting a1275 in at some point.
And if you don't put flares on that car (or just *tiny* ones), you can run vintage with it too. Radiused 1973-style rear fender (like mine) are fine for most vintage groups.