The 302's in vans are likely more similar to those that came in trucks. And no, they are different HP and specs than those that came in the Mustangs - they are not HO's. Unless they came in the big, brown van -- with UPS on the side.
Just as a tip if you are looking for "mustang spec" motors; the '87-'89 lincoln LSC has the same longblock as '87-'93 mustangs, 225 HP & 300 ft/lb TQ right from the factory.
I just picked up a free 302 roller-cammed motor from a friend of mine. It came from a van. I've never before heard of a factory roller motor in a van. Hmm.
Some of the trucks/vans/sedans had roller motors - don't know the year break. But that's only a very small portion of the issue. I think the seller was suggesting the motor was just like the Stang, and as has been pointed out above, once the heads, cam, pistons and portions of the intake are changed, then it's 'just like' the Stang. Kind of like George Washington's axe.