With a garantee, from a trustworthy source, it's worth a lot more than an engine that was "running when I parked it"... meaning when it stopped, I stopped. I have seen a bunch of those.
I drove my 39 deluxe for a bit when I first got it, ran ok... Turned out that it had cracks- real BIG ones, in three cyls. Glad I did not try to sell it...
As is, figure two out of three times that a core is likely to have major defects... People don't usually remove these things til there's a reason...
$100 to $1500 Karl