Exhaust has now been modified - two new mufflers installed. Doesn't seem to have changed the idle noise much but certainly much quieter at speed. Not quiet, but quieter. It's at least now possible to have a conversation over bluetooth which is good. Doesn't seem to have affected the power much which is also good. Now just gradually building up the K's until the first service which is 700km or so away. Thinking about doing the transmission as well which looks easy in theory. Should probably do the diff too if I'm going to finish the cars big birthday properly.