73 360 Ignition timing after Chain replacement

You have an engine that is nearly 50 yrs old. Quite possible & likely cam has been replaced & the new one has more oomph. Which would explain the need for more timing at idle for best idle quality. If you did inadvertently install the cam 4* advanced or retarded, doesn't mean it is wrong for that engine. Could be, but only way to know for sure would be to put the engine on a dyno & test all three cam positions.