Where do I find a tri power linkage system for Holley carbs on a 1956 Y-block motor?

Answer 1

Try here.

Answer 2

Yikes--that's a tall order. I don't recall a 3-duece set-up
as OEM to any Y-block and if there were they would be
very rare and expensive. I think you should check with
more contemperary stuff like the set-ups for 340 &
440 Six-Pacs or tri-power GTOs and Corvettes. The carb
spacing can't be much different so modification should be
easy. Also, try Lokar. They make all sorts of stuff like that.
Some tweaking on your part may be needed but anyone
who knows what a Y-block is shouldn't have much trouble!

Answer 3

hemmings.com