If your rider who races you wouldnt have much problem with the cut off time...its 4 hours and thats plenty.
The biggest issue is suspension and possibly a long range fuel tank, there is club fuel stops every 60km, (mad crazy part of the race track where the guys see fuel depot and cuts you off to get in,,,or they just pull out without looking) with a bigger tank and few extra people you can have our own camps and 2 stop.
Suspension needs to be soft to soak up the whoops and you bike jetted so you go flat out but not sieze with taller gearing.
My RMZ450 was geared to do 160km/h for long hard pack road sections.
An Evo bike would go ok with the longer suspension,,,,you could make it on a pre 78 but would be slower so as not to break your spin
Tim