What track in TX? I'm familiar with Maxton, that's a ways from here. I was figuring on county highways out in the country by my grandparents for testing. But I'm guessing there'll be some major jetting differences for altitude.
I've got a basic outline for the bike: 650 head, maybe crank, fairly aggressive porting, 750 carbs/possibly pistons, hot cam. Aluminum wheels (stock hubs), no front brake/disc, race battery. I want the average guy to look at the bike and think I'm running a mostly stock 550. Stock seat/tank with side covers. This is my guess at the minimum to hit 120 up there, and probably just barely.