what skill level would be needed to play ddivertimento for marimba and sax?

Divertimento for Marimba and Sax is a great piece. I perfromed it in a recital only last week. I guess that the tricky part is not the six mallet passage, but more so the continuity of sections. There are a few sections where you play in one register of the keyboard, and in no time at all you have to shift down the keyboard. I have found this to be the most significantly taxing part, if you want to pull it off well.
The 7/8 section just needs a little slow practice at first but you'll get the hang of it pretty quickly.

Best of luck, it's a great piece to play. Oh by the way you need to find a sax player who can move their fingers very quickly!!!

Cheers,
Richard.

also i have seen a jazz version of this song with the same name, but is it the same song?

i don't know how this compares to what your playing but two of my friends just played i think its called Song book for marimba and sax
Good luck with divertimento