Hiya!
I had the same problem when I got my Ragdoll about 6/7 weeks ago. It took two weeks. From the pair of them growling at each from opposites sides of the room. To being put in the same box for a three hour car journey. Let them scrap, but seperate them if they start being really noisey.
I found my original kitten would wait for me to go to bed, wait till I turned the lights out and he would pounce on Freija. I would put whichever of them started the fight in their box if it got out of hand and 9 times out of 10 it was Icky. Also when I went out, I would take it turns putting one of them in their box. So Freija could explore her surroundings safely but then Icky wouldn't feel put out. There was one side of the room Icky would go skitz at if Frieja went anywhere hear. But once she had wandered round there freely and put her scent over it, he stopped bothering.
I'm nowhere near expert at this. As these are my first two cats. But I thought everything was doomed and it sorted itself out quite nicely. Now they won't be out of eyesight of one another.
X