I have the same set up, except I have a t350 tranny. The 305 and 350 are very similar in specs. GM said the 305 was the economical V8, while the 350 is the power. The 305 saved people money on gas in the 70/80 gas shortage while still giving people the opportunity to say I have a v8. You have a 5300 lbs truck and the 305 won't get it up to speed very well. You're better off finding a junkyard and rebuilding a 350/383/454, money situation dictating. If money is not an issue, buy a new fuel injected LS motor.