That's the EGR control valve. (EGR started in 73 which is why your 72 didn't have this device.)
The purpose of the EGR system is to reduce oxides of nitrogen (NOx) from being released into the atmosphere which is a good think for the next generation.
There isn't really any performance reason to remove it. It's only active at light cruise and is disabled at higher throttle positions. Looks better without it, but no reason to do so for performance.
I'm assuming he's still running the original carbs? Because if not, I'm not sure where he's going to hook up the ported control vacuum signal...
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