I did what you are planning to do on my 512 Eddy dual quad motor in my 69 RR. I bought a Hybrid fiberglass A12 six barrel base so I could seal up the airbox on the underside of my six pack hood. I cut out the center of the fiberglass base, ground off the edges of the Eddy air cleaner base, and mated the two together using epoxy and rivets. Now I can use the oval air filter and lid. Once the lid is on nobody knows the difference. Mine still needs some finishing before painting. The spacing on the Eddy manifold carb center to carb center is diffrent than the Hemi. which is why the repop bases don't fit the Eddy manifold. I did talk with the owner of Hyrbrid fiberglass and he said he could make the base to fit that manifold if there was enough sales to warrant it.