Honestly...how good was the 318...mpg / durability / hp

I put together a 318 from used parts that ripped. Later roller short block. Flat tappet racer brown cam and lifters that had laid around the garage since before I was born. 360 j heads,edelbrock performer and a thermoquad. Used 340 valve springs with.030 shims. It stomped 5.0 mustang's in my 73 4wd d150.
Unfortunately the cobbled up air cleaner jammed the throttle wide open and I missed a shift . The tach read 7200 when the valves hit the pistons and the fire flew.