I'd have to look up the RPM where it was rated for its maximum HP, but I definitely wouldn't exceed the factory-rated max RPM by much, if at all. If the carb helps it breathe for better torque without over-revving, no problem, but the lower end simply won't stand high speed without stretching rods, or other catastrophic failures. The pistons are extremely heavy, and put a lot of stress on the rod bearings at speed. If the engine doesn't have some sort of governor, I'd suggest fitting an electronic rev limiter to it once the carb size is increased.
Jerry

Edit:
I don't have specs on engines prior to 1974 handy, and by then, the 401 was not an option. The 379 V-6 that year was 170 HP @ 3600 RPM, with max torque of 280 foot-pounds @ 1600. The 478 made 192 HP @3200, with 371 Ft/Lb @ 1400. They're definitely low-rev engines, with absolutely no advantage to increasing the operating speed.
Jerry

Last edited by Hotrod Lincoln; 08/24/2008 1:19 AM.
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