Regarding the 'decompressor setting', on the AVL engines, this is a mechanical device which actually lifts and holds the exhaust valve open very slightly. As long as you have some free play in the cable and in the operating mechanism, you should be fine. There is no way of adjusting this set up anywhere else - it is a collar around the exhaust cam follower, which is located by a snap ring. It could only go out of 'adjustment' by excessive cam / follower wear, which is pretty unlikely.
B.W.