Putting the oxygen sensor bung in was not too tough. I did have one problem with a burn-through, then I had to pile on more material and to clean that up, it got pretty thick. I’m pretty sure it’s sealed, but it’s not particularly pretty.

The sensor is placed on the left side of the collector. It is not exactly gases from all four cylinders impinge on it, but it sits directly between the pipes for cylinders 1 & 3.

I have plugged the bung with a suitable spark plug and after I get a piece of bike inner tube to cover the chrome bit of the muffler, I will deliver the system to someone who will shot peen all the paint off it. I can then paint it with a decent high heat paint like VHT Flameproof.