what is the best way to rebuild a 305 with more horse power the motor now has 170000 miles on it and when i hit the gas the oil pressure drops instead of getting higher and i want more horsepower i have a 96 k1500 z71 and i do often play in the mud i have the stock transmission but i have 4.10 gears in the rear if i upgraded to a crate 350 would i have to convert to a carb or could i still use my fuel injection what should i do build the 305 or get a 350 crate motor

You can use a crate engine, everything will bolt up. The 305 and 350 are the same block, with the exception being the bore that the pistons and rings ride in. From what I know, you can actually bore a 305 block out and make it into a 350, but from what I know its fairly costly to do so. Another thing, upgrade the transmission, you can easily pick up more power. Other things would include investing in a power programmer so you can adjust things like the transmission shift points, along with other points of interest to gain more power, but they run about 400-600 for one, but its a good investment if you want to make it into more of a play toy than a daily driver.