No that's a big ripoff. Don't buy it, you can get a better deal on ebay if that's what you want.
BTW, where are you located, what's the name of the paper, and does the guy selling the motor list his phone #? If so, could I have it? I'd like to.....ummmm.......call the guy and tell him how he is trying to rip someone off.
A big block for $250 is dirt cheap....power pack heads was a name given to a certain small block head....I would look into it more because the wrong use of the name and the unusually low price doesn't sound right.
If it's any good yes, if not you're stuck with an expensive chunk of scrap iron.
I have a '66 427, when I got the block it was never touched, it was taken apart and sat for years, it had what looked like little rust in the bores but it turned out the rear two were pretty bad, two shops turned away and wouldn't bore it for me, one shop did, it had to go .060 over, thats no problem for a big block but the point is the block was almost not usable. The front bores were standard and could have been honed and used, just to point out how good the block was before it was improperly stored.
So you're going to need to look it over real good, $250 is a real good price for a good rebuildable big block.
I payed $400 for a '68 427 shortblock that's already .040 over, been sitting in my garage for a year now.
If you decide you don't want to buy that big block please please give me the guys phone #. Bad part most of those deals end up being some small block or not even a small block. To some a 4.3 v6 could be a big block.