[old Chevy guy]

Dont sound like to bad a price if its garanteed not to knock or smoke ,But if its the correct moter to fit in a 55 its not the right moter to fit a 68 and even if the guy gives you the parts to make it fit if its really a 55 it will be way more trouble than its worth. I could be wrong but I dont think they made a 250 till 63 or later ,at any rate the bell was diffrent before that. I had a 61 with a 235 6 cylinder and my buddy told me I could swap in a small block and I knew he had done this in his 66 .Well there was hell to pay diffrent bell, moter mount brackets clutch pedals linkage you name it ! 63 and up easy,older stuff not so.whatever year he says it is make sure it has the standard chevy bell bolt pattern like a small or big block v8. I found out the hard way on my first chevy moter job on my first chevy truck.Hope this helps some.