One of the guys at May Madness, Steve Fyfe, got 448. 2 hp with his original, way over 100K miles (maybe 140K?), 175 hp engine and injection pump. I helped him with a few pump tweaks and he has 370 injectors and the HX40-16. All the modifications have been mentioned repeatedly on this forum. His truck is another of the daily driven vehicles that tows a big trailer out here.
Stock delivery valves and fueling section. We changed the torque plate, AFC spring, governor springs/seats, timing. Ported head for egt control, ATS manifold, remote BD exhaust brake.