Differences between a Cat 3406b and a 3406C

A friend of mine has a Kenworth T800 with a 3406b 425hp 43mg,thats getting tired , there’s some new 3406C 310hp 41z comming up for auction in a week, is it cost effective to buy one of these C ,s or just rebuild the b, don’t now the differences between the two,thanks in advance

Differences between a Cat 3406b and a 3406C