I would advise you to get a compression test first. If compression is too low, you may have valve problems or your piston rings may need to be replaced. You have a fairly high mileage bike. Let's say you have to offer a price considering you are likely to do some major work on the engine pretty soon.
Keep in mind that it is quite likely that you may have a hard time to find even common spare parts and make sure you get a Service Manual.
I found quite a few at
http://www.davidsilverspares.co.uk/parts/genuine-spares/and quite a few on
http://www.cmsnl.com too
If you can't find it there, I would say good luck on Ebay.
I drive a Honda CM400T 1980. It did look perfect like yours, but after 500km I lost compression on one cylinder because a valve oil seal was defective and piston rings on that site failed. Rubber parts just don't last that long. I had to get the engine valves, cylinder and piston rings restored to specs because I was fortunate enough to find all required spare parts.
I don't think it would be wise to assume you will be able to safely ride this 1975 motorcycle for a long time without spending a substantial amount of time and money on finding parts and labour.
My first bike was a 1971 CB 175... I loved it.
I would advise you to consider finding a Honda CM/CMX250: Lower mileage, very reliable, easier to find parts because they were made from 1980-1987.
Good luck