Greco are set neck, one or two pickups, 3 point bridge plus a tailpiece the shape is patterned after the original '60s Reverse with a bit of a hump on the upper bout. The pickups are (at least on mine) monstrous, with great lows and mids - they are worth the price of the bass! Slightly shorter scale and a bigger neck, almost P bass.
Orvilles are also set neck, true 34" long scale, 3 point bridge, slim neck like a '76, there are at least two variations of pickups in them, some are TB Plus with chrome covers ( which is what mine had) and another design that I have not heard but understand that they sound quite good. Epiphone's Elitist models are direct descendants of Orvilles.
The two are quite different, I like them both for different reasons, so just buy one of each.
I think Orvilles are overlooked, mine has been a great mod platform.