You could do a minimum pathfinder team with one rail rifle for three points more than your marker drone squad, I believe you save two points by taking the Ion rifle but I will have to go double check.
By removing the marker drones, you could then take off the target lock from your commander, as I don't anticipate many situations at a 500pt game that you will need to be able to shoot at two different things with that unit.
Dropping bonded would grant you an extra firewarrior and a third, or an extra pathfinder with a point to spare. For the record, I always bond everything as a matter of principle, so I am happy to see someone else bonding firewarriors.
You could also drop the drone squad and try to work in a piranha, which should be easily doable if you also drop the bonding knives.
Edit 1: Do you have to maintain the same load-out for each unit, or can you stack on extra wargear/models later?
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