Welcome to the bolt, stinky. I agree, the 305 isn't enough engine for what you're doing. If you want to stick with the GMC V-6, get a 351. It's a lot better engine. Will give you a lot of bottom end. For speed you will have to do something with the gearing. Your 4.10's are the best you can do with the 10 bolt rear. The swap for a newer 14 bolt isn't too bad, usually requires welding on new perches. But you can get 3.73gears, possibly even 3.42.
another option on gears is to install a spicer auxilliary tranny, which can get you an overdrive. The Clark 5 speed is another option, if you can find one with overdrive and afford it.
If you haven't already, go to Jolly's website
www.6066gmcguy.org and look around. Quite a bit of info on this series of trucks.
