You have more to check than only the engine. Sails, rigging, moisture content in the hull,... In my opinion, you can save money by purchasing the 1970 after having the engine checked by a professional if all other things seem equal. Even if you have to repower, at least you will know you have a new engine. I can''t imagine spending $25000 on "any" Centaur...and I like Centaurs. You must be in the UK or Canada...Eh?