Lyle, you can see the stringers when you open the doghouse. The motor mounts are bolted to it. They'll have a whiteish appearance - back then, CC did use wood, but they also covered the wood with a fiberglass material of some sort. You'll see it there.
Have a look at the stringers there. Any flaking, cracks or chipping is probably not a good sign. Also, tighten the motor mounts with a wrench - they should still bite tightly. The floor is a little tougher to check - basically walk every inch of it and try to feel for soft spots. There should be no squeaks. You can peel the carpet back a little under the doghouse too. Have a look there.
If you're deadset on buying an older Nautique, buck up $150 for a marine survey. Certified marine surveyors have equipment that can tell you whether the floor/stringers/hull is sound or not. It's not that much money, and can save you thousands in the long run.
There, how's that for some tips? Hope that helps. Good luck.