Try my base. It is a cut to fit - one szie fits all type base. I've equipped many single 4bbl Hemis.

Price is $175 + ship and accessories. Machined aluminum bridge is $75 and is used to hold assembly down. The lid studs thread directly into my base in the front and rear- there are provisions for 4bbl AND 6bbl lids... your choice (there's a chrome 6 pack lid out there for sale). The nuts glassed in to the left and right of the opening is where you will mount the bridge and that helps it clear if you need to drop the base quite a bit as it doesn't interfere with a choke horn. PM me, they are in stock and I have everything else to complete the assembly (except the 6 pack lid studs for the moment - you can always simply use threaded rod cut to size to save a few bucks).