The closers are more of a cylindrical part, rather than the 'top hat' shape of the 2V part. Openers are similar. 4V pieces are a bit smaller too.
Never been into a 2V head, so I don't know exactly how it would compare. The 4V closer springs are quite stout.
The closers seem to get a good grip on the split rings and valve, it takes a bit of tapping to get the closer to slide down the valve enough to get the split rings out. I recall 2V folks saying that the closer clearance is just right when you can still spin the closer on the valve. My 4V closers won't spin on the valves, even with the closing rocker pushed down till it's up against the cam.
One of the local dealers offers a shim kit:
http://www.europeancycle.com/catalog/index.htm
Here's a couple other sources:
http://www.emsduc.com/pages/1/index.htm
http://www.motostrano-store.com/du2vashkit.html
They all look like the same stuff, at least on my monitor..and all seem to be about $290 for the 4V kit.
I inspected the kit at ECS, and they looked a bit crude compared to the OEM stuff. I bought their closer measuring tool, and it's a decent part.
IMHO, you
cannot measure the thickness of a 4V opener with a regular micrometer. The sharp corner of the spindle bottoms out on the inside corner radius of the shim counterbore, or even hangs up partway in. Gives a totally erroneous reading.
My Starrett micrometer won't fit, and I'm
not about to grind down the spindle on it. I made a little tool (similar to the closer tool) that sits down in the counterbore properly, just like the valve stem does.
I've done all of the maintenance on my cages and bikes myself, other than the very rare occasions when I didn't have the tools or couldn't find the problem. I can count those events on one hand, over a span of 20 years. I don't like other folks working on my stuff either...... :-/