Public Transport v Private
There is no such thing as a public transport C of A from this year that is relevant to you. A Public Transport certificate will only apply where paying passengers and freight is involved. To find an aeroplane therefore with a public transport certificate it will be due for a full C of A inspection almost immediately, therefore an expensive time to buy into it.
To train in an aeroplane it does not have to be maintained to ' Public Transport'. The last inspection must have been undertaken by a licensed engineer and a 'Release to Service' issued.
Being a Cherokee the engine will have a TBO of 2000 hours with a possible 50% extention taking it to 2400 hours or longer - on condition, if no training was to take place form then on, that wouldn't matter.
ADF's are a real problem but a new one is very expensive and with the threat that many NDBs are due for closure, perhaps a poor investment right now. I wouldn't advise joining any group that wasn't set up to maintain the aircraft and equipment to licensed standards. Old equipment well maintained can be more than adequate. FM Immune is a must if IFR flight into controlled airspace is on the agenda. Some will argue that FM Immune is legally required for an ILS outside of Controlled airspace, they could one day be proved correct.
As to the condition of the aeroplane and equipment in question, speak to the engineer who maintains it and look into his eyes as you ask the question. What arrangements do the group have to replace the engine - don't walk into a large bill from the off.