Steve,
It can only be a 351W GT40 lower. Plus, it looks like it is aluminum. There is no other 351W lower that would bolt up to a GT40 upper intake. It also has a 1” phenolic spacer.
The only other 351W lower intake that would bolt up to a GT40 is a marine cast iron intake. Which is the basically the same, just a different material.
I have seen the 351W Lightning GT40 lowers sale for $650 up to $1000 on different websites lately. The tubular uppers go for $350 and up. The lightning intake cover are going for $250 and up. Basically, the complete intake is going for north of $1000 these days. The first generation of lightning’s are becoming popular and people are restoring them. So, these intakes are becoming harder to find. A few years ago, I had three sitting on my shelf. I dold them all for a lot less than they are going for today. Also, the sum of the parts Is what I was looking at.
I think it could be a decent deal if you can talk the guy down a little bit due to it being an used motor with an unknown history. Again, I have no skin in the game, Just wanted to share.