oh geeze, um... gas mileage, lol, hp is so much easier to guess than that

but id say, if you run around a 9.6:1, with the vortec heads, cam, and a 750 carb, you could expect around 12-17mpg, but i really have no idea, carbed engines really arent my focus, and i dont really have alot of experience with the vortec heads on carbed engines, those heads are really efficient, so they might boost mileage a bit, but i dont want to give you a higher number and possibly lead you on. dont wanna say you got a shot at 20mpg, then you put it together and get like 9mpg lol, youd come back on and bash me and id loose my rep, then id cry and it just wouldnt be good

but yeah, mileage is a hard one cuz it depends on so many variables. type of driving, if you commute or just do saturday afternoon top down drivin, if your a lead foot like me, what kinda gas you use, what the air is like, how the carb is jetted, everything. but i feel that 12-17mpg is a good guess, maybe, and i stress maybe a bit more because the design of the vortec heads are so efficient at making more power from a given ammount of fuel. but i honestly dont know.