which motor to use

I am building a gto clone from lemans and have original 350 but can get a 400 with correct date for car which one should I bulid ?  

I am partial to the pontiac 350 yes the rebuild kits cost a little more but have the potential to be great performers.
Plus you already have it and the money you would spend to buy the 400 then rebuild it would probably cost more in the long run.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

It all depends on how far you want to take the GTO clone thing. If you don't care past the appearance items, then build the 350. Like Pontiacman8 says, they can be very reliable and potent performers. If you want a more authentic clone, go with the 400.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Be careful on the year 1975&up 400's had weaker main webbings.
 
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Thanks I think I'll go with 350 and possibly make it a 383 stroker if I can find the right info on the best way to do it.  

Remember you don't have to stroke it to make good power but it's up to you.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I've heard alot of different opinions on building a 350 and would like to here yours
if you don't mind thanks  

Well I have built a lot of 350's and the 350 is a good foundation for anything from a mild to wild combo and are capable of making some serious power and torque.
It all depends on what you want and how much power you are looking for and your budget.
I do not recommend the stroker kit it is just not necessary to make a decent and respectable amount of power. So far the most powerful pontiac 350 built to date at least that I have seen did not use the stroker kit it used the stock crank.
The stock cranks are pretty strong and a properly prepped crank can handle just about anything you can throw at it. The 350 blocks can be safely bored to .060 over without any problems.
If you let me know what kind of power you are trying to achieve then I can list some parts that will get you to or close to your goal.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Any thing else just ask.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Thanks, My son and I just finished a 69 firebird with a 400 and being new to pontiac's (was chevy guy till now) I am very pleased with the power that motor has.
So now I'm starting my 1968 le Mans convertible and it has the original 350. I want it to be quicker than the 400. I can't let my sons car beat mine that's just not right. I'm not looking for radical just good clean reliable power. Any info would be greatly apprieciated. Thanks.  

Was the 400 built to stock specs list the specs of the 400 and the head casting numbers and then I can come up with a combo for the 350.
Also list the head casting numbers of the 350 as well.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

The 400 is basically stock .030 over to clean up and edelbrock intake performer everything else is stock. I will get the 350 in a week and let you know the #'s thanks again, Darin  

Any time.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

It should be fairly easy to come up with a combo to beat your sons stock 400.
hopefully the 350 has a good set of heads on it.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

THERE IS NO SUBSTITUTE FOR CUBIC INCHES,EVER, A 350 AND A 400 BUILT SIMILAR 400 EVERY TIME
MOST PEOPLE OVER REV,OVER CAM OR OVER CARB PONTIACS.  5800 RPM WITH STOCK COMPONENTS   19LBS OF WEIGHT DIFFERENCE BETWEEN A 350 AND A 455
YES THERE WAS A 4 SPEED AUTOMATIC (HYDRAMATIC ) IN THE LATE 50'S AND EARLY 60'S