D2 is a non-wing Midget classification. 1000cc "upright" Mini (or Lightning) Sprints are legal to run in most, if not all "D2" associations along with stock block 2.4 liter automotive engines like Chevy Ecotec, ford Duratec, etc. The 1000cc Motorcycle engines and the 2.4 automotive engines put out roughly the same horsepower (200-240) on methanol with electronic or mechanical fuel injection. There really is no official "D1" designation but if there were it would refer to the USAC/POWRi "National" Midgets with purpose-built aluminum block engines (like Esslinger, Fontana, Stanton/Mopar, Toyota TRD) that put out around 450 horses.
That's about the gist of it; Montpelier lets everybody run together with very open rules and some weight and tire allowances for stock-block and motorcycle powered cars and the Midwest Lightning Midget group (I think that's what they call themselves now) is formulating a rules package somewhere in between "D2" and Montpelier.
Or you could run at Waynesfield or with MMSA strictly with other 1000cc Lightning Sprints, mostly wing with 5 or six non-wing shows sprinkled in.