I wouldn't recommend it. I've measured my blood pressure on 25C-NBOMe and it's much higher than when taking stimulants even in huge amounts. This is likely due to the vasoconstriction this and other NBOMe series psychedelics cause. I've mixed 25I-NBOMe and Amphetamine before, and I had fun, but the vasoconstriction was pretty severe and I wouldn't repeat it.
In my experience 25C-NBOMe causes greater vasoconstriction at a similar dose than 25I-NBOMe, and Methylone at a normal dose also causes more vasoconstriction/higher BP than Amphetamine does for me.
Methylone would definitely mix great with a lot of psychedelics, but I'd go for something physically safer really since even if you get the dosage right there's a good chance you won't be able to fully enjoy yourself due to any side effects you experience and worrying too much.
If you must take the mix, keep the dosages of both much lower than normal. I'd stick to like 500ug-600ug (sublingual/buccal, less with other ROAs) of 25C-NBOMe max, and 100mg Methylone. You wouldn't need much of either drug anyway since they're both euphoric and will potentiate each other.
Still my 2c is it's not the best idea.