diff gears size

[340pete]

hi i need to get lower gears for my ute, in it now are 3.50's
408/727 9" n/a
28" high tyre
1/8 mile 8.2@88mph
bogging down 2.000 60ft
no wheel spin
6000 rpm in second gear over the 1/8 finish line
will only be reving it to 6200 rpm
need to set it up for the 1/4 mile
any calculations out there???
thanks in advance, peter