Never heard that explanation before but it sounds good. You can dump everything in the photo, just be sure to plug the hole in the manifold that delivers exhaust gas to the underside of the plate. Alternatively, many manifold gasket sets come with a SS block off plate to block the center exhaust port between the head and the manifold. It's on the pass. Side head only. Sounds like it's too late for that. If you don't block the hole the exhaust gas will burn up a paper gasket. You should use a gasket with a steel shim similar to exhaust manifold gaskets. This is what the factory used (but with a hole for the gas passage). If anything I would think performance is enhanced even slightly as you're no longer introducing hot dirty air. The compression is so low on the engines that I'd be surprised if you experience detonation. Agree the fuel mixture and timing should be adjusted for optimal spark plug burn. Finally, be sure to cap the PVS port that supplied vaccum to the EGR valve, or disconnect altogether. This valve works on temperature and if connected to vacuum will open at temp. if still working. Use ported vacuum for your distributor advance.