If the normal maint has been done then I would say there is nothing to worry about. At that mileage I wouldn't suspect anything is going to go wrong but if anything, the chain tensioner 'may' have to be replaced by 150K (?). I did mine at 140K. This is just me but I think your motor is just settling in/broken in.
Even tho my fav local dealer is very, very small (6 techs) they have never had to replace a chain on a M117 or M119 V8 motor (I was told). They have several 200,000+ mile cars that they maintain. And when I bought my V8 with 100K all those years back I had the same concerns as you.
The chain will most likely audibly let you know it needs help. Drive sensibly and change oil often and there should be no problems. Those are my 2 cents.
