trying to install my stock crank in a 350 but when ever i tighten the main caps the crank locks up and i have checked that the main caps are in the right order any help would be great thanks

 

are the main caps facing the right way?
are you sure you have the right bearings?
try tightening them one at a time see if you can turn the crank

 

there all facing the right way and im using the standard size bearings for it its a its a 3970010 block and a 3932442 crank and ive tried tightening just one cap at a time andsoone as i tighten one it locks but when i was tearing it apart the first time the crank spun freely with the old bearings in it so i dont know

 

You may have mis-labeled oversize bearings. Did you measure them (thickness)?

 

sometimes the fillet on the crank requires narrow bearings.