That I'm afraid sounds exactly like mine did.
I too thought it was a lifter however they are solid lifters with shims.
Honestly, don't waste your time looking from problems with the head, cambelt, water pump.
Keep driving the car and soon you will develop a misfire and lots of grey smoke (un burnt diesel) from the exhaust.

The problem is little end failure - I know, I didn't believe it either!!
If you're in any doubt then take the sump pan off and see how much bronze material is in the pan!!

The knock tick knock noise is actually the gudgeon pin floating around in the the end of one (or more) of your rods as the bronze bearing is starting to disintegrate.

Take the head off, on mine you could move number two piston clockwise and anticlockwise with your fingers!! On removal of all pistons number one piston was starting to show signs of wear / play. Three and Four were perfectly ok.

Just doing the same job on mine and it's an engine out job as you cannot access the pistons with the block still in the car. The ladder plate which is bolted to the bottom of the block can only be removed once the bottom end is on the engine stand. Head off and pistons out through the top.

You cannot buy the little end bearings from Ford as they do not sell them. The choices are:
1) New Conrod and Gudgeon Pin from Ford at approximately £180.00 inc Vat (this price is for one rod and one pin only)
2) Find a local machine shop and have some new little bearings made and pressed into your rods
3) Find a breaker that'll sell you second hand rods, pistons and pins complete
4) Find a company that'll sell you a remanufactured rod with bearing already pressed in (you'll still need new pins as yours will now be all wonky)
5) Second hand short motor from a breaker

It's a pretty big job for what is essentailly a small bearing but that's life.
I've done a lot of research on this of late and I guarantee you that will be the fault.

Matt