AHRMA has always had a twins class that allows all twins to run it, never had a vintage or year set on that class so it is pretty much a Ducati cup class. From the AHRMA rule book:
http://www.ahrma.org/rulebook/sec10.htm
10.9 BATTLE OF TWINS®
10.9.1 Machine eligibility: All competition classes are intended for two-cylinder motorcycles only. All classes may be run together and scored separately as determined by the number of entries and track conditions. Classes include (see rule 10.11 for additional mechanical requirements):
a) Formula 3: Pushrod OHV machines to 1000cc, OHC 2- or 3-valve to 800cc, OHC liquid-cooled 4-valve to 650cc. Suzuki SV650, Buell XB9R and Kawasaki 650R limited to Supersport specifications (see 10.11.1); otherwise must compete in F-2.
b) Formula 2: Pushrod OHV machines to 1250cc, liquid-cooled OHC to 750cc, air-cooled 2-valve OHC to 1000cc and air-cooled 4-valve to 1000cc. Ducati 748 and 749 4-valve water-cooled must race in F-1.
c) Formula 1: No displacement limits. Engine modifications are unlimited, with the following exception: water-cooled 4-valve twins over 900cc are limited to Supersport specifications (see 10.11.1) and intended to be U.S. road legal production models only.
d) OPEN Two-Stroke: Air-cooled two-stroke motorcycles to 500cc; water-cooled two-strokes with tubular frame to 400cc; and modern 250cc GP type machines.