I think the 98 Kilauea was designed for a fork of around 43cm length unloaded (crown race to axle centre) - i.e., that's roughly the length of a Judy SL (63mm) or a Z2 (70mm). Equivalent to c41.5 with a rider on board. The period P2 was 41cm long and I think the 03 Unit still had a 41cm P2, but you might want to check. No surprise that you find that ok, as you wouldn't notice the fractionally quicker steering.
I'd expect the Manitou 4 to be a bit shorter than 43, but not so much as to cause you severe problems. How long is it out of interest?