which new/rebuilt engine

[cam]

I recently puchased a 70 gmc lb with a 307 and a 4spd tranny. My situation is the engine is tired. I've looked at the cost of having it rebuilt $1500 or buying a new gm goodwrench 350 $1360. I really like the fuel economy of the 307 and was wondering if anyone had purchased the goodwrench 350 and put on the stock 2barrel manifold and carb. If so, how did it work out? what was the mpg difference from the smaller displacement engine?

Thanks!