Will dual snorkel air cleaner off a 3rd gen 5.0 fit a holley 4bbl? And fit under the stock hood of my 79Z?

It won't fit a dual-feed Holley... the air cleaner base hits the float adjustment nuts.

They sell spacers, I used one to mount my Blazer's original air cleaner box with cold air tube to a Holley 4010 a long time ago. I had to modify the bottom of the air box since it wasn't round, it had those triangular indentations. Other than that it worked out wonderfully. :D

You'd need at least a 1" spacer to do it (I know, I have that air cleaner and have tried this)... will you have room?