They're both fine brands, either one should be a fine bike. Mountain lx was either above deore (deore existed) or you mean something like exage lx which would be below deore, either way performance will depend on the shape the bits are in. If they're in good shape then they'll work. I have a full rigid mtb w/ 500lx derailleurs- below deore- and the stuff works fine.

W/ the kuwahara you might want/need to buy a new fork and you would have trouble finding a) a threaded fork and b) a fork w/ the amount of travel you need, likely 50-60mm or something I would guess. If the heattube is 1 1/8 then you could switch to threadless but you'd still have a find a small travel fork.

The u-brakes on the chainstays suck but otherwise mtbs from that period were overbuilt, really, and will last forever.