[fred cook]

I believe what you have is a set of SSIs for an engine with the mechanical fuel injection. This pipe supplies hot air to the thermostat "stack" that expands and leans the mixture as the engine warms up. Just plug or cap the extra pipe.

Good luck with your project! Watch out for rusty/stubborn exhaust stud nuts. Do a search on the BB for info on safely removing the old nuts without breaking studs.