I am planning to run a modern 4 barrel on my 354 Hemi so here are some pics of modifying the intake. Because the intake has no material in the areas where the new studs go, I'll make a 1/2" thick aluminum adapter plate that mirrors the gasket shape. But the hard part is done, increasing the bores in the manifold itself. You can see the scribe lines to get an idea of how much had to be removed. I used a Cyclone annular cutter in my mill.....a 100% completely chatter free operation. The left side holes are only about a 1/2" deep cut but the two holes on the right side are a full 2" drop so the long cutter really came in handy.
Are you putting a spreadbore on, or is it just perspective? The nearest hole looks bigger than the rest.
Most folks would be amazed at the performance difference when you open the manifold to 1-11/16 to match the generic Holley pattern. I have been doing this for years and using the old 3310 for most installs and the 850-950's for the hot rod jobs. I have about a dozen manifolds on the shelf if there is any interest. As for a spacer, there are plenty on ebay for about $15-$20. .
My gasket and carb measured 1-3/4" so that's what I machined it to. I'm making a space as the ones sold, that I've seen, don't have threaded holes for the studs. Are there any that do? I don't want to mess with those thin nuts they usually use on the underside.
only square bore spacers I've seen are non threaded, a friend threaded his and used reducers for the 5/16 studs and had drilled it to adapt his intake but his carb stud reducer st up came loose quite often .. looks like you got the tools to make a nice one!
If you used an Edelbrock, you'd just have to install longer carb studs, where they have the small pattern.
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