I would have thoght that 1200hrs is ok. It wouldn't put me off, but I was just highlighting potential pit falls.
To qualify the above, if its 1200 hrs since new the corrosion is your enemy as this is over a long time.
If its 1200hrs since O/H...who did the o/h and what was done to the crank /cam etc.( In theory they could have been cleaned,inspected and put back into service with new shells etc,if they were "within limits").
Worse case...1200 hrs since rebuild...could mean stripped cleaned and put back together as was i.e. no new parts.
Bottom end parts for the 0240 are scarce because they were only ever fitted to a few Condors and Reims manufactured Cessna aerobats(FRA 150)
At worst if the engine goes bang you can replant a standard o-200 as a straight swap but you will need a prop as well and that lot is likely to set you back more that the plane is worth.
On the other hand, you can use theses facts to barter with the vendor, maybe fly it 10 yrs with no trouble at all. in the meantime try to buy any spares that may become available.
As a guide, there were many more aerobats produced than condors with the 0-240 and I imagine over 50% of them have been re-engined with the 0-200.
I am not scare mungering, just helping you to go into this with your eyes open. ANY a/c is a potential money pit, but lots of us do it so there must be some reward!