I did a set for myself years and years ago, back in 1991.
I used a 906 casting, and opened it up to max wedge and ran it as high as I could go to right before the spring seat area. Then tapered it down from there.
It made quite a bit of difference. I just cut the ports off of a stock valley pan and silicon'd the edges to the intake manifold. I used an M1 that I also raised the roof all the way into the plenum.
It was alot of work, but in my Charger it picked up 3.5 tenths...and I did mill the heads down from 85cc to 82cc so it wasn't all head work.
This was an 800DP on a flattappet 440.
Car weighted in at 3820lbs. with me!!
It went from 11.72 to 11.38 with only those mods.
Brian