You obviously haven't thought this through. You every looked under the hood of a Toyota mirai? You would need to replace all electrical and mechanical ancillary equipment. All the looms. Even the wheel hubs if you want regen braking. The entire drive train basically needs to be replaced. Different heaters, AC compressors, radiators and cooling systems. Then you need to find extra space for the battery. Yes that fuel cell needs to power a battery which then powers the motor. You would be left with the chassey and the cab basically. The amount of labour cost would be higher then a new truck. But heaps more GHG