I had 214,000 miles on my old motor and it still ripped a 14.2 quater mile time. The only reason I rebuilt it was b/c i only had about 10 pounds of oil pressure at idle, but it never smoked or anything.
ive seen a few 265,000 milers on here doing good. its all how its been treated. am i wrong or couldnt you have the stock block bored .0030 over to make it a 306, so you would have all new cylender walls? that would seem really cheap next to a new shortblock, but hey if your not driving it all winter then thats plenty of time to have a completley new engine built. if the chassis is in good shape then buy it. you cant go wrong.