could look at an iron case A833 OD. my duster has one with 3.23's and I love love love it. gears are a bit wide spaced (3.09/1.67/1/.73) but cruising 70 mph at 2100 RPM is wonderful, and with a moderate cam (thinking 224-230@.050), a 408 should have no problem with the gear spacing and running at that RPM in 4th..