Thanks man good reply, answered my question. I guess I should have worded it differently from the jumpmmm... I see. Well, when you can swap gears and add traction, you don't need a whole hell of a lot of power to run a low ET. However, just after the finish line, that new GT is going to blow your doors off because it's trapping a lot higher.
If you want the equivalent power to keep with it even from a highway roll, or to match traps in the 1/4, I'd say a solid 300-320 rwhp.
I think that's underestimating the '85 significantly and overestimating the New GT a little. I'd guess the 85 mustang weights quoted were 4 cylinder LXs. You're probably close to the same as the '87-93s. It's the same chassis, motor, and a close enough body.