[wilf leek]

Good Grief Simon, you are going through it, aren't you! My sympathy, FWIW.

With a non-operative exhaust valve, you will have generated some "interesting" pressures within the affected cylinder. Head gasket would be suspect, also your noise may just be something as simple as an exhaust gasket blow. I would also be concerned about the health of the affected rocker, lifter, and pushrod - they would have taken quite a beating.

You would be very unfortunate, IMHO, if you had cracked a piston skirt, or otherwise damaged the piston in that cylinder, but it could happen.

Only one way to be 100% certain - pull the affected piston and inspect it and it's conrod bearings.

Did you do a compression check on the affected cylinder? Or a leak down check? Data from these could be illuminating.

Just think how much advice you will be able to give others once that thing is sorted! (sorry, just trying to look on the bright side).

If it makes you feel any better, I shall be swapping out the diff on my car sometime soon, and that is not a job I look forward to.

Luck

Wilf