... Any guesses, should the holds just be bored straight or tapered?...
I would bore the holes, turn the pate upside down, and radius the edge with a radius router bit or with a milling machine.
I used to make billet Stromberg 2bbl carb spacers years ago and had them featured several times in some magazines. One was a dyno test on an early Chrysler Hemi that used 4 of them on a 4 x 2 intake. They did before and after tests with and without my spacers and saw a 20 HP increase with them, or 5 HP per spacer basically. I radiused both the top and bottom edge of the throttle bores on each spacer and it does make a difference. I also made a 60MM spacer for a sheetmetal intake for a friend of mine years ago also that I radiused both sides of the bore. He asked why, so I made another one that was not radiused and sharp on both sides. We took both of them to another friend that has a flowbench and asked him to compare the flow on both of them. The radiused one flowed 125 CFM more than the unradiused one. Both were the same bore size to within 1/2 a thousandth, and the spacers were the same thickness to within that same amount as well. Radii make a huge difference..... That's why many cylinder head race teams use radius seat cutters for valve jobs instead of angled seat cutters now....
I say now, but they have been doing it for more than 20 years now!
