ok as you all can tell i am not very fluent in motors but what i do tell ya'll is what i know i don't know that much about the engine this is my first truck i'm only 17 looking for a way to make my truck better. the crap inside the engine is removeable but not without a lot of work. it came from water getting inside it. i'ed scrap it if i had the money to get me a better one but i don't so this has to suffice the rest i really don't know about. the timing IS off a little or so i beleive because both my grandfathers build engines hotrods from scratch (no lie) and they both said so. the carb is aftermarket but we did take it off the 350 and put in on the 305 the 305 came out of an 85 van. it was the best thing running for the price. i geuss the gas mileage is good. i just didnt realize it. i get about 14 mpg give or take a few. its duel exhaust it doesn't y off the carb has 4 "holes" in it and the cam i don't know about it is an 82' chevy silverado "305". its not 4x4 i wish it was in a way 4bbl? powervalve?i don't know what your talking about. vac advance inop?well thats all i can say for now so later!