You are quite right ... was not the first ... first to do so if the mass in USA, but not the first.
I do not doubt your word, but your date does not fit me ... sure that it is May 61 and not May 60? .
If you mail me your pass I can scanned the brochure catalog 1959 where are all the first "H references, from H1 to H18.
H1, H2, H3 circuits are the first 1:24, the first car-free and without a transformer, the second with 1:24 cars and Mercedes Benz F.1 but Jag D processor, the third reference to the same circuit with transformer).
You can also pass scan of the brochure catalog 1960 with the first circuitry 1:32 ... H30 and H31 (are the same circuit, both with and Maserati 250F Jag D 6V but two of the second circuit with transformer).
But later in the year 1960, due to the high price of the circuits, 312 circuits are created with low D 2 Jag benefits ... I have the flyer and notice of such a circuit in October 1960. Subsequently, the 313 (but not exactly when).
In May of 1961 when I start to see the first circuit in my opinion Ferrari Testa Rossa third car, although I can not find in my bibliography circuit USA 9940, but yes the 9950.
(Apparently, with the sale of the Tootsie ... exactly is signed March 17, 1961 ... a change from the reference point - 2 digits or 3 digits for the case of economic cycles, a 4 references digits)
I can spend a lot of information by letter, photos or scans, but not always mine.