This is how it would be mounted on a 70 L78/LS6.

The guy that I got this stuff from had 2 LS6 Chevelle engines many years ago, so this must have come off of one of them. I had a chance to get one of the carburetors and lots of other stuff, but got there too late. I see that this Y block would not work with these lines. What would the Y block be from?

69 L78 and L72 used the Y-block but not with those fuel lines. Both of those fuel lines look like the 70 version.