I hav read in a review that ek 240 aio is difficult to fit in the gigabyte z490 itx ultra due to vrm heatsinks... i would happily go for custom build, but i intend to move it around and i can guess it will be a lot more expensiveThe Phoenix MLC is all end of life, as the EK modular products always end up. They killed the Predator, then the Phoenix, now they've also killed Fluid Gaming (their Aluminum stuff). I would not suggest buying anything EK that isn't either a CLC or a standard copper-based watercooling part.
I spent a really long time being chicken about watercooling, worrying about doing a custom loop and trying to convince myself that these modular systems (like the Eisbaer/Eiswolf from Alphacool or the Phoenix from EK) would be a solution, but your problem is your tubes are going to be too long and with chunky QDCs in the middle that take up space. In the end, if you want to watercool in a 280, it's never been easier with the new Aquanaut pump/block or the Alphacool Eisbaer LT pump block. You'll be much happier doing it yourself rather than using kits.
If all you're after is a 280 CLC for the SM580, there are lots of better options, like the new EK 280 AIO or the Fractal Design Celcius+ 28 Dynamic.