i got an blue print engines vortec 383 long block
one peace rear seal.summit raceing say to use an
400 style balancer for one and two peace seals
but 3 months ago when i ordered it summit sad to
to use 350 balancer with one peace and 400 style with two peace.   what balancer do i use.
and why did summit make both of them 400 style  

just curious....

did it come with a blue print spec sheet and balance card...  every balance job gets a card written out...  that is where the weights are calculated to build up the bob weights.... that will say which balancer is needed ... a 0 balance or a 400 balancer...

the numbers written on the card will match the numbers stamped into or painted on the front of the crank ....  

You have to find out if the crank they used int he shortblock was an externally balanced or internally balanced crank. If external, use a 400 balancer, if internal, use a standard 350 balancer.

Since most of the stroker cranks today are made for intenral balancing, I'd guess you need a standard 350 balancer, but contact the manufacturer to be sure.