So quick update, no more check engine light! w00T w00T!!
The car has now officially passed Georgia emissions, easy peasy lemon squeezy.
Turns out I had a vacuum line in the wrong place basically. The fuel tank vent/purge line was the problem, for convenience I plumbed it directly to the intake manifold which on the Porsche motor is about how it is except that it has a purge valve on it so as not to create a vacuum leak.
Seems that the Chevy motor didn't like the extra fuel vapor/vacuum it was getting and was causing the idle to be "higher then expected", even though there is no noticeable difference in the idle. Once I re-routed the line and fired it back up, light was gone, YAY.