Depending upon what service the original owners wanted that bus to do it will either be geared low for round robin shuttle driving while never going very fast or it was an activity type of bus that was geared for highway driving.
I am not a big fan of Cat engines in trucks and buses. The 3126 had some real issues when they first came out. Most of those issues were ironed out while still under warranty. But the fact remains that service is harder to find than for a Cummins and the parts are sold in gold boxes for a reason--you will need a lot to pay to take the part home.
The fact the bus has tinted windows and coach A/C should be a big plus for you while transporting dogs in the hot months.
Good luck and happy trails to you!