Do you have a mill? Can be done without. Simplest and cheapest way to get a 4 barrel manifold. https://www.jalopyjournal.com/forum/threads/331-intake-manifold.993980/
Yes I have mill and lathe . I am blessed with a bunch of equipment. having the time to use them is another matter . I have seen a few good looking home made cross overs and some really bad ones to made from galvanized water pipe fittings and such . I'm studying that 331 2bbl opened up to a 4bbl in your link . It looks like it was milled down a lot to get a bigger base and then opened up . I cant tell 100% but it looks brazed inside ?? A couple good ideas in that linked thread I had not seen it . Thanks