I don't think the Ironman FCPs have a dedicated maintenance cycle. They are a much less "fussy" shock than a set of Icons since they don't use pressurized gas, they have rubber bushings instead of heim joints, etc. They weigh probably 2X as much a set if Icons too - super beefy 2.8" shocks with a steel body.
For mine personally I'll just rebuild them when the back starts getting a bit bouncy. I'll be pretty happy if I get 50-60K out of them prior to a rebuild and ecstatic if they make it to 70K. Riding in my buddy's Tundra did make me want a set if Icons for a bit, until I read your tread and remembered that I bought the FCP shocks specifically for the long service intervals

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FYI, I have a spare set of front FCP shocks. Ironman did a warranty replacement on my front coilovers as the springs were contacting the shock body (and I had bought assembled coilovers) and let me keep the old ones. They new coilovers have a shorter spring - apparently this was a common problem they rectified. I'd be happy to sell you the front shocks (they would need new springs) and I am pretty sure they'll bolt in your 460. PM me if you are interested.