Mate if your engine had 2550 hours on it and was in the condition you said ( I assume there was zero leakage from the valves during comp check) then certainly can be released again for 100 hrs or less if you wish.
The fire extinguisher - now that is a item fitted permanently to your aircraft, possibly post from the factory without an EO to fit it as it was done years ago.
* So that is a dilemma in its self, but the fire extinguisher as with every component in an aircraft has inspection and maintenance requirements. If the airframe manufacture does not list these compliance times you then go to the component manufacturer for this info. Many have a 6 month inspection inc a reweigh that needs to be done with calibrated scales and some have a monthly check also.
* Now many persons that have say Charter C210's use CAsA schedule 5 - but they must do that 6 month reweigh on the fire extinguisher or that aircraft is illegal to fly.
So where is the LAW that says a charter aircraft on CAsA Shedule 5 requires a fire extinguisher to be reweighed but a private aircraft not - NB a private aircraft does not require one to be fitted but if fitted it must be maintained.