Eddy heads. Can I/Should i...?

The vendor bought them for a 340 and has decide they are not right. I have not checked yet,but i thought 340 heads=63cc and 360 (...779) heads 65cc.
My real issue is wil my motor benefit from these heads in its current state of tune?

the 360 have the 63 cc and the 340 head has a larger chamber.