fitted ok it was a bike i raced in the UK last year
gear ratios all wrong and didnt seem to suit motor power
my 5 speed 465 was a million times better but i suppose
if there is no 5 speed availiable you may have to use it
i have a 4 speed rm500 and the gear ratios are excellent
so its not just because its a 4 speed
but you could try it and see a 465 barrel and head
bolt straight on to a 490j bottom end