Dear Jon;
None taken.
I'm not familar the (450 Hp) engines you mentioned. Were talking of a 60s 150Hp engine and trying to add as much as possible, on a low budget.
My point is simply that ANY "re-combination" of the exhaust gases (flow) defeats the goal of what your trying to acheive with headers.
Perhaps; not in total like you say, but even "in part" is a waste/misdirection. The pipes need to be separate for best results.
Happy trails.