I keep thinking about those turbos. Since it looks like you’re still fabricating the hot side I’d suggest, above everything else in this thread, that you stop and verify the specs on those before you proceed with the downpipes and waste a lot of time. To me they look like uncontrollable boost, and too much back pressure to make power past 4K rpm on a 400” engine.
You could find suitable replacements for under $200 each…not including wastegates.
