first off..that pinging nosie you hear..is your valves..you need to adjust them..and to answer your question on the two clutches..yes..one is for power take off..the other is for transmission..most honda 300's i've worked on..i rebuild the centrifugal clutch..but..seeing the age of your bike..your going to be in that side anyway..you may as well replace all of the clutch disk and clutch arm pads on both of them...kill two birds with one stone so to speak...you can try to just replace the tranny clutch disk..but..if it were me..i'd do both of them sinse the cover will be off..those gaskets aren't exspensive..but..no need in taking the chance in tearing it up twice..if you can get all your clutch problems fixed at one time 
..oh.and yer right about the nosie could be your timming chain..you can replace it if you want..but..a easy fast fix..if you don't want to tear into to it..is to take your timming chain slack adjuster out..get a piece of flat metal..wrap it around the end of the tensioner..make sure it will fit into the slack adjuster hole..then..before you try to slide it back in..crimp..or what ever you can do.to make sure it stays on the end..after you do all that..bolt it back on..yu'll need to take the center bolt out of the slack adjuster to take the slack out of it..takes a small screw driver to fit in..turn it as your putting the slack adjuster back in..this is to be able to get the bolts started..once you get it bolted up..start it up..and see if the pinging noise stops < this is if you haven't adjusted the valves first >..try all of this..see how it does...oh..make sure you get that metal crimped on good on the end of that slack adjuster..you don't want it to fall off into the engine ..if you decide to just put a new timming chain in..and need any advice..just ask
..oh.and yer right about the nosie could be your timming chain..you can replace it if you want..but..a easy fast fix..if you don't want to tear into to it..is to take your timming chain slack adjuster out..get a piece of flat metal..wrap it around the end of the tensioner..make sure it will fit into the slack adjuster hole..then..before you try to slide it back in..crimp..or what ever you can do.to make sure it stays on the end..after you do all that..bolt it back on..yu'll need to take the center bolt out of the slack adjuster to take the slack out of it..takes a small screw driver to fit in..turn it as your putting the slack adjuster back in..this is to be able to get the bolts started..once you get it bolted up..start it up..and see if the pinging noise stops < this is if you haven't adjusted the valves first >..try all of this..see how it does...oh..make sure you get that metal crimped on good on the end of that slack adjuster..you don't want it to fall off into the engine ..if you decide to just put a new timming chain in..and need any advice..just ask 
