If your timing cover is modified to have a hole in the front you can access the gear without having to pull anything off the front of the engine
With radiator in place

At least thats how my engine is set up

dattoman, that is the only way to go, what benefits did you get from it.

What I really would like to see is dyno graphs before and after fitting and tuning these pulleys.

This would give a good idea of what they can do and what the repercussions.

I also have a removable plate on my one timing cover for my adjustable cam gear, for me it isnt about doing power adjustments, its more about dialing the cam in where it was specified to work. Your cam will be a regular regrind, thus if its over 290deg the chance of it being at optimum cam timing for your setup is fairly slim.

2nd what Rezlo said, it's more for dialing in the cam rather than moving the powerband,

in something like a GSX750 you can advance or retard one cam to play with power, win some loose some,

Ok now it starts to make sense to spend the money.

What is the stuff to look out for when purchasing such a pulley or when getting one made from a original one?

When converting the cover, what tips and tricks do I need to know about?

A cam gear with adjustment through slots can come loose, a multiholed gear wont move but is harder to adjust as you have to remove the chain, (easy on l-series), both have pros and cons, and yes it is for dialing in aftermarket or reground cams.

Ok guys I was at one of cape towns better tuners. I know he does the tuning on one of south africas fastes 140z fitted with a L20b with a z22 crank and so on. The car made 158kw but after dailing in the cam to that puuurfect spot its making a mind blowing 174kw! So yes my L will have one as we are running the same cams.

mmm, some of my favorite numbers mentioned there

Yes, and once you find it where it runs best, to make it perfect, order a new cam to match your findings. It will be even better.

You use the adjustable sprocket to test a camshaft that is not optimal. To find out what your engine needs.

For fine tuning (which won't result in huge power gains) you may need to "dial in" the cam. You can use offset keys to do this, because you'll never need to adjust it again once dialed-in.