I'm going to be another voice of doom and gloom, but as the saying goes, if it seems to good to be true - it usually is.
First off, if it's a $1730 bit of kit he's willing to accept $1150 for it, that's pretty much a 33% loss he's making. If he's that desperate for money, I don't see how he can afford to pass up so much. If it's a gift (and in your first post you say he bought it, the gift bit came later - was that you or him changing the story?) then clearly he's got a friend or relative with enough spare cash that they're willing to buy him an expensive computer he doesn't even need - if I was in his position I'd say thanks, but could I have the cash and they return it? Or at the very least, could they loan me enough to cover whatever bill is SO urgent that I'm willing to lose out on $500-odd. His story may be that that's why they gave him the receipt, but again, if it's been paid by card then that wouldn't work. The only way he could get the cash was if it had been paid for by cash - in which case he'd just be able to return it.
Anyway, if you are still set on going for it - and I really do hope it's all legit and it works out, by the way - then there's some precautions you really should take.
First, do NOT go alone. Take at least one buddy, preferably two. I assume you'll be paying cash, in which case this person knows you're going to be walking around with over $1200 on you. It's not unknown for someone to rock up to a deal like this, only to find themselves mugged by the "sellers" accomplice(s). So take one pal with you, and another to keep an eye on you from over the road, ready to call the fuzz if needed.
Second, don't get distracted - it might all be going OK, only for the seller to suddenly get an "unexpected" "emergency" phone call, resulting in the sort of rushed, "ok man, I gotta go - do you want it or not? I haven't got time to mess around" situation where you're so caught up in it you're not paying attention.
Third, if at all possible (and this does go back to number 1 really) do all the checking first and THEN go get the cash. That way if you get mugged on the way to the deal then they won't get much.
Lastly, check his ID. Don't tell him you want to see ID beforehand - let it be a surprise. If he doesn't have ID on him, see what his excuse is. If he does, well that's up to you to judge if it's real or not. And make a note of his name and address - if he protests, WALK AWAY.
Oh, and just because he has a receipt and the box DOESN'T mean it isn't stolen. You could still end up out of pocket if it's somehow tracked back to you.
Like I say, I really do hope this all turns out well, but it's just too fishy for my taste.