Any of the older Zentradi pods still around?
I assume you are using the downsized Zentradi, given that you are looking at the newer iterations of the pods. However, a while back, I had a couple ideas for what to do with the older pods.
1: Remote operation...basically drone units. the original pods, while carrying decent firepower, were hardly examples of pilot-safety conscious design. Dropping a drone-rig into the old pod lets you use it for things too risky for a flesh and blood pilot, as well as gives you another use for the old mech.
2: Major refits...Lets face it, the original Zentradi weren't exactly tiny. Relieved of a pilot little shorter than the pod, frees up an enormous amount of space/weight. It shouldn't be too hard to fit a decent amount of structure reinforcement, upgrade the armor, and add a reinforced cockpit for a Human operator...might even have room for a few missile tubes.
Both ideas benefit from the canon fact that literally MILLIONS of the bloody things were built at one point or another. Even without new manufacture of parts, the supply should be fairly good.
O0
Now, the older pods aren't likely to be that popular, even with refits. So they'd most likely be assigned either to training ops, (As Op-For) or as a punitive assignment. Piss off the brass, and spend a tour pushing rusty tin.
Of course, now that you are on Rifts Earth, beggars can't be choosers, and every mecha counts...even old ones.
The character I had in mind would be one such pilot. Battloid pilot, good stick, but with a talent for irritating the brass, so he got stuck in a refitted Officer pod with a number of drone-rigged standard/artillery pods slaved, and tasked as op-for for training rotations. Good for his piloting skills, as he got a LOT of stick-time, but a dead-end as far as promotion goes. Not sure what race to make him though. still considering that.