I believe  that is a  'dot4'   or  354.4   perkins. 


Highly doubtful you'll find that  balancer assembly new.    Every   dot four engine in the salvage yard will be missing it's damper!!   HIghly sought after!
I had the exact thing happen to my   3545  MF with the same engine about  4 yrs ago.. with zero luck finding a new one.    "No Longer Available". 


But,  I happened to find  www.damperdoctor.com out of Redding Cali.  that   rebuilds them.   
  He cleans them,  indexes them,  and  injects new rubber under vacuum to cure them.   Mine has several thousand hours on it, and still runs perfectly true. 
At the time,   a  'good used' one was about double in price  of  his repair.  About the only drawback I can see, is if your belt grooves are worn,  you are stuck with them..   maybe  now,   they have  re issued a new replacement.

IIRC,   certain  drive belts with  exotic  fibers  put out  a fair amount of  static electricity..  which degrades the  rubber bond..  May have to look that up again to confirm.