I've gone a 1.85 in our Pure Stock Y-Camaro...but it's a pig, though, at 3700+ pounds...I believe COPO Pete has gone high-1.7s in his COPO Camaro? Like John mentioned above, Terry has bettered that in his FAST Camaro, and waaaaay bettered that in his FAST 'Vette!
And you gotta run the same size front/rear tire regardless of which class you decide on. Let us know how the test outing goes...
BTW: you'll have to stick with the 400thm if you wanna run in Pure Stock.