best refit for the cyclops 10Z, drop the AC 20 for an AC 5, adjust armor to about 17 tons or so.
makes the mech tougher, and while it loses it's "damn big gun" the AC 5 gives it more long range firepower to defend at a distance, instead of trying, and failing, to be a faster Atlas
That's when I would argue a PPC would be a better choice. Same tonnage and range as the AC/5, double the damage, no ammo concerns, only 3 more heat than the original AC/20 so more can go into armor. But this is also where we start going into fan design territory so I'll stop there.
As for swapping out the AC/20, the CP-10-Q does swap out the AC/20 for a second LRM-10 and 7 tons of armor which isn't bad.