Timing chain is often the problem on your unit- it wears just out of reach of the tensioner and sometimes makes noise. To change the chain- you do have to remove all the way past the wet clutch- which means more gaskets also they have to clean and re-seal the rocker cover and double check and possibly adjust valves. Also if you have a worn out chain- I would think they are changing the oil too. By my rough estimate you would be at about 300 in parts and its a solid
3hrs- to do it properly. And depending if they are charging the diagnosis time with it and shop supplies and ect. It sounds like they are fairly close on your quote- maybe slightly high just to cover themself from the terrible under quote.
Just my opinion