What gear for 6K in 1/4 mile?

With a 28" tire (275/60), you may need more than 4.11.

Converter slip can make it tricky to figure too.

If you have some idea of what the car will mph, there is a good calculator here.

http://www.wallaceracing.com/calcmph.php

From your combo I am going to guess 105-110 mph with a good tune in the carb and timing figured out. This is a guess, so if that's lower than you think I mean no offense.

According to the calc, 28" tire, 4.10, 6000 RPM = 121 mph.

Same numbers a 4.30 gets 116 mph, 4.56 gets you 109 - all these get drug down by converter slip a little. Moper is probably right about the 4.30 with your combo.

As an alternative, you could go 4.11 (easier to find) and if that isn't enough, maybe go to a 26" tire?

Sounds like a fun combo. Good luck!