What kind of oil pressure does your shortblock make? Can I fire it up and run a compression check on it? No. Unless it's running in a car, you're going to have a problem moving it for that kind of money. Without knowing any of the above, why the in HELL would someone assume your 30K shortblock is in better shape than a 100K mile shortblock?
I suppose someone who's really interested would take the time to pull some rod and main caps and really look at it, but even then, how are they to know you didn't gouge a cam bearing putting in that nice $300 cam?
You can disagree with me all you want; I'm just giving you my honest opinion as to why you're having a hard time moving the thing. Why are you selling it anyway? And in response to your original question, I wouldn't trade for a 351W.