I like the Irwin......
if condition is the same, and I'm a C27 owner. There is a pretty good Irwin owner's association. The basic Irwin 28 sold for 20k in 1976, the same generation cat 27 sold for about 15k. Count up the amenities, the most important being condition of the engine. You'll also want to compare things like holding tank systems, battery systems, shorepower and charging systems, rigging, deck hardware, (new or old winches) Sail inventory and condition, underwater bottom condition, (pay a diver to take a look).... electronics, instruments, is there a dodger, ground tackle and storage. What about the galley, has it been upgraded from the old princess stoves.... the list goes on. All these things were extras. The 28 came in a swing keel model, check to make sure you know what yours is and whether it's a feature you want. Here's a link to Irwin Yachts website.