Howdy Ponyman,
You can use ANY 200 from 1965 to 1978. (after '78 the bellhousing has a rolling change).
All you need to do is to use your 170 waterpump, pulleys, oilpan, oilpump pickup tube, exhaust manifold, etc. Your C/4 and it's flexplate will bolt right up to any of those years.
You'll probably have to fiddle with the throttle linkage. You will need the 200 distributor (larger diameter hole in the 200 block) It is a good time to add a Duraspark II. If you get a post '69 engine, grab the carb too. Your 170 carb won't bolt onto a 1970+ head w/o adaptation. You might want to add the alternator that every engine had after '65. It's only a matter of splicing a few wires.
I hope this helped.
FYI We have 3 1/2 pages of detail on this swap in our handbook.
Good Luck