realy nice looking truck
jegs sells a brandnew GM 350 for not a lot of money
http://www.jegs.com/i/Chevrolet-Perf...rentProductId=
its pretty basic cast crank cast pistons but 4 bolt mains and a 2 piece rearseal
with all the stuff you have on youre 305 now you should have about a whole new longblock under the hood when youre done
if you want more grunt i would go for a 383 with an eagle or scat rotating assembly and some vortec heads and some sort of cam meant for towing , that keeps the rpm low , if you build the machined block together youreself you prolly could do it for about 1500 to 2500 dollar depending on the machinework you need done to the bare block
check some of the hotrod builds for details