Messick's is showing a replacement for that part number. The other dealer shows K77700-00844 as the correct one, so who knows which one is actually correct at this point. Personally I'd go with the higher CCA because I'm in Massachusetts and we get some cold winter mornings and I'll take all the CCA I can get for a diesel. I think we've thrown enough info at him where he can make a somewhat informed decision on a replacement battery CCA.
Dave