The Star League didn't have bigger ACs than 20, no Ultras nor LB-types.
I did DL Redemption and Malice but i've no idea where i placed it, think i need to read it...
EDIT Found it, quick search for Pallas gives only one line with it. "...the upper body was that of a Pallas, a design
long lost over the centuries."
Nothing else is said about the Pallas, though given the context, we can assume it is a design in the assault 'Mech class but no weapons were given for it.