What will my 68 Dart 408 run in 1/4 mile?

You have an assload of clutch. And no way to tune it. Your shocks leave about everything to be desired. Not sure of MT nomenclature but that looks like a radial tire.

So your tires will hate an assload of clutch, untunable shocks and most likely a 9.45 overall first gear. That's if you have a 2.66 first gear box. If it's a 2.44 first you will have a 8.66 overall first gear which is powerglide and less first gear.

I'd skip the two step and slide the clutch like a mutha humpa at the starting line. The last thing you will want to do is beat the crap out of the tire.

You have enough HP to run low, low 11's if you can make the chassis happy.

Not bashing your stuff. It just looks to me like you've got a lot of parts that will hate each other, and really no way to tune it.