Planning to chassis dyno the 517 in the spring and hopefully (if time allows) do some manifold/carb/ignition testing as well.

I was gonna say if you want to send me your manifold I could radius it for you, the turn from the vertical plenum wall to the runners in both the front and back is a bit too sharp, work the corners for a more gentle turn both down and then out towards the ports. you don't really need to enlarge the ports themselves beyond the plenum,
I wouldn't even try doing that because the roof of the lower is the floor of the upper and the casting is pretty thin between them. Plenty of meat where I'm referring to though.

Beyond that I also enlarged both plenum halves and took the divider down a bit more. I run a 1000CFM Pro-Systems carb on it, it's very responsive, but tough to get it to hook, even taking off in second and I shift it at 6800.