Why assume a bored out 270? 150 thousandths (5/32) is a long way to take a block. California Bill lists a 292 jimmy build in his famous speed manual. Destroked 302 for higher revs and certain cubic inch classes.
With the picture shown, we could only guess at what engine is in the vette at the time of auction. Mecum doesn't know what it is either. Definetely a gmc block. Likely a 270 or 302 with a ton of work.
What I find most interesting about the engine picture is the generator placement. I have never seen one on the passenger side.
