I have no familiarity with CAT engines, only Cummins, but I have not heard of any disqualifying comments about that size and vintage engine. CAT engines are well built and reliable overall, and if there is a weak point (and every engine from every manufacturer has one) it may be the fuel pump from that vintage.
Do you know the actual model of the engine?
My suggestion to you is to use the rule of thumb for horse power vs weight. Generally, it is recommended that you shoot for 1 hp for every 100 lbs. of gross vehicle weight. Just a recommendation, not a hard and fast rule. It puts you in the ballpark for a motorhome that meets your overall needs for towing, cargo capacity, and performance.
99% of the motorhomes you will shop for, of that vintage, will have the CAT or Cummins engine. Later built engines, post 2007, CAT got out of the over the road market, but that had nothing do do with their reliability.
IMO, the brand of the engine should not be a deciding factor, only its current condition and record of maintenance.
Larry, Eileen, and Finley
2004 Alpine 36FDDS
Third motor home, first Alpine, no need for another.