I`m about to rebuild my motor and want to build a combination high horsepower and high mileage engine. Or as close as one can get to that combination. I`m starting out with a 400 small block bored 30 over and ported and polished heads. Where can I get a spec sheet on the rest of the parts I need to make this happen. How about a turbo or supercharger?
Any suggestions are appreciated.
Thanks Quigley  

A turbo will give you the most power while keeping good economy.

When you say high mileage, what numbers do you have in mind? Also, what car is the motor going in?  

The car is a 84 camaro and I would be happy if I can get in the high teens with the mileage and still be able to have some fun with the car. Before going bad the motor put out aprox 380hp. I never really checked but I would bet I wasnt getting any more than 10pmpg on the average.  
Thanks Quigley  

Gonna be tough to get high teens with that big a motor, it's all gonna be in the rear gear and trans you use.  

55guy is right with thta big of a motor it will be hard to keep high gas mileage. First off tru to remove all the things you don't need in the car decreasing car weight= better gas mileage. Electronic ignition is another plus. The more efficient the explosion in the combustion chamber the better gas mileage you will get. Transmission gears are crucial the more gears you have the better gas mileage you will get. Don't go extreme on the cam. Stick to something will a low idle and that goes up to about 5500 rpms. if you are going to run the turbocharger first off it's going to be expensive because you have to get custom headers and you will have to lower the compression ratio so you can compromise for the extra air being put into the combustion chamber.  

Dear God, don't use a 400 block....
350 4-bolt +.030", 400 crank, zero deck height with a .020" shim for a head gasket, aluminum heads with 200cc runners and 64cc chambers, 1-3/4" hedders.....
add a healthy hydraulic roller cam and some roller rockers.....skys the limit bro