Looks like the adjuster hole plug is on the brake drum on the outside. I originally thought access was at the rear.
And there is some 6x10mm bolts holding the hub to the spindle. These have to be removed.
Will the notch wheel move in either direction?
Did you apply some penetrating oil?
PM your email and I'll email you directly, this may take some time to fix.
And the exact model would be useful. It's a 03/04 TRX350 but is it a FE, FM, TE, TM version. Might make a difference.