I saw the round style CBX 1000 swingarm on eBay and it looks very similar to a CB900F.
I know from experience that the CB900F does require narrowing at the pivot, the pivot hole on the frame does require enlarging and you will need a pivot bolt made to fit. While doing the narrowing of the swingarm make sure that you have proper sprocket and tire alignment. I used the rear wheel of a CB1100F with the standard CB900F axle and spacers.
The CB900F is about 2" longer this may require additional shock length since shock angle is changed. I used the CB900F length which is 365 MM (14.37")