Just as a data point, I made my own 4-1 with 30 inch primaries and a slip fit collector. I have one of the primarily tubes welded solidly to the collector and the other three are retained to the collector by the often seen tabs, bolts and compression springs. I have one solid link hangar at the aft side of the sump bolted to a tab welded on a primary in front of the collector. It should also be noted that I have ZERO ball joints anywhere in the system and the flanges are welded to the primaries (no slip fit at the head) and the whole system is mild steel. In other words, its built just like drag race headers have been done for the last 50+ years, and I have not had a single crack in 400+ hours of service.
...and I also have about $200 worth of materials and a weekend of fabrication wrapped up in the whole thing.