I'm needing some help on an engine. I've got a 350 sbc in my 65 C20 right now. I'm using it as one of my dailey drivers. its drinking oil and or throwing it out somewhere. The anti freeze keeps going down every 3 or 4 days also. I've just run the numbers and found out its either a 73 or 74 model engine. 155 to 160 hp.
I'm looking at getting a new 350 sbc but don't know what HP to get. Ive heard to stay away from the 290 HP as its not good on gas. jegs has a 260 Hp engine that might be ok. I want some power but really want better fuel economy if thats possible. i'm getting on average 12 mpg and have been for the past month loaded with tools and sometimes pulling a trailer with carpet on it to install.

ive got an edelbrock 600 cfm carb and edlebrock intake on it.
it has a 400 turbo transmission. not sure of the rear end. I'm just wanting to get a long block.

mark