[philminotti]

Just a guess, but being an EFI guy, an educated one...
I suspect that can is a common vacuum "plenum" for your eight stack system. I assume your running EFI, yes? Your system may have relied upon a MAP sensor as a proxy for engine load in its VE calculations. With eight stack, you need a relatively clean vacuum reference, thus the billet reservoir. The capped vacuum line could have connected to a MAP sensor. As these schemes don't often work all that well, especially with big cams, perhaps the EFI was retuned to run an alpha-N scheme, which only requires RPM and throttle angle to determine fueling, thus eliminating the need for a vacuum reservoir and MAP sensor. Just a guess.