Force has a lot of range, lots of GRs, and is Chaos March '64. UAC makes sense for Chaos March 64, since the WoB is active there and the FWL is selling them to anyone with money or credit, but tactically I'd take either a GR or LGR, since I wouldn't pick my commander to have a weapon with shorter range than the remainder of his unit, and with no many GRs lying around it seems more likely they'd have had a spare handy than rustling up a whole new UAC10 (unless it was a package deal with whoever sold them the Sunder).
I know everyone (but me) hates them, but two ER PPCs and an LGR would give it the range to support the Victors and other ranged heavies without exposing itself too much, yet still give it a period feel.
Of course, since its an Omni, if you fight multiple battles in your campaign you can just do all these things on different days, celebrate the Omni nature of the mech.