The ticking noise can be a few things

I had this on my old 24 and the 1st thing i looked at was the zorst manifolds, but having had both done...still had the ticking noise!!

The other opinion is that one of the Head gaskets has developed a leak which is an engine out, and both heads done job

Apart from that, i dont really know!!

I ended up part-exing mine in for a 200 but would have liked to have known what was up with the old girl!!