You can probably go ahead and move the live rock too... there definitely isn't enough there for the Mandarin to feed on... I have over 70 lbs. of live rock in my tank and I still think my Mandarin died of starvation (though I'm still not sure).
Most of the places I've seen that sell Mandarins recommend that you have at least 100lbs of live rock or more with a healthy copepod population.
If I were you, I'd temporarily move all the stuff to the 38, remove the UG filter in the other, allow the 75 to settle back down and then move everything back. You can then probably leave a bit of the live rock in the 38 to let it cycle with a grocery store peeled prawn or something.
This way you don't have to worry about the 38 being fully cycled, since you'll be quickly moving all the specimens back to the 75 within a couple days... which should avoid any cycle-related stress in the 38.
That's just my opinion though.
Also (just FYI) typing in all caps on the internet is considered yelling... and you don't want to yell at us, do you?

Hope that helps.