another option is a Tremec 5 speed (the rpm's at 80 with 4.10 gears is 2500, the 6 speed is overkill)

there is a thread here
https://board.moparts.org/ubbthreads/showflat.php?Number=5899467

it requires major chassis mods including modifying your torsion bar cross member as well... not for the lighthearted