I follow this fairly precisely:
http://www.rwbsmith.plus.com/citroen2/E ... 6vhead.pdf
page 12 just about sums it up but it mentions something I think most people miss and that is that some components should be lightly "greased" upon reassembly. Not enough to block oil circulation, but greased not oiled.
Burping of the tappets is important and is one of those things that's easier to see being done than to describe in words. One addition I did which I feel played an important part, was when I reassembled, I was doing an engine that had been stripped by someone who hadn't bothered to keep the tappets identified as to where they came from, so I had to hand fit every one and 16 things being fitted in 16 holes gives a wide range of possible combinations.
When I eventually was satisfied with where I had placed them, I greased as per instructions but then went one further by trying to roughly align the hole in the side of the bucket with the hole in the head that feeds it. Now whilst I know there's nowhere that says that this has or needs to be done, my reckoning was that the closer to alignment these holes were, the less distance the oil needed to travel through the oil groove that feeds it and the more constant the oil pressure would be to the tappets. I found mine were extremely quiet on that job.
Another thing I found interesting was when I set the cambelt to 100% accuracy (so described due to the way the pins slipped so easily in & out even after the engine had been run) by using a camlock in conjunction with the pins, I noticed that the intermittent rattle when first started had disappeared. (Don't ask me to explain that one)
The only time we have ever had to replace hydraulic tappets in one of these engines was when not only were they noisy, but also the engine was also losing oil pressure due to the amount that was pouring out the sides of the buckets.
Price will make your eyes water as you get two prices; one for the buckets and a second price for the actual internal piston. Out here it costs more for a complete set of tappets than even we can ever hope to get for a decent car, so I'd imagine over there whilst still a lot cheaper than our prices, still will be a somewhat daunting cost.
Hope that's some help for you.
Alan S