Take a look at these...
http://forums.luvtruck.com/viewtopic.php?t=12255
http://forums.luvtruck.com/viewtopic.php?t=12356
http://forums.luvtruck.com/viewtopic.php?t=10702
http://forums.luvtruck.com/viewtopic.php?t=10636
and maybe that will help.
If you have a choice...personally I would go with a switching to a 5 speed transmission and building up a bigger 4cyl engine. Partly to be original/different...and partly to get more bang for your buck without ending up too nose-heavy...or drastically altering the power-to-weight ratio or cornering ability/handling of your truck.
Just my $.02 worth.
Whatever you decide...please keep us all posted about your progress!