Size and version should be on the valve cover side/outside when on looking at them installed on the engine, it's on the float bowls.
One bowl will have a big EW and the other is stamped with the info. The stamping is quite small.
They will work on a 3.0 just fine. You'll likely have to re-jet them and depends but you might need bigger venturis. If they are weber venturis the size is cast into them and you might be able to see this looking down the throat.
I'd invest in a WB 02 meter, it will save you a lot of jetting guesswork.
Also be aware a lot of tuners (like me) use jet reams to size jets, so while the size number may be correct, they also could be way off. You can buy jet size gauges.
I'd go over to the Performance Oriented site and read all the tech pages.
For parts the best price and selection I found is
http://youroil.net/weber_carb_parts.htmlThey are the east coast PMO source and it's a much easier to navigate than the PMO site.
BTW besides the versions listed by mskala they could also be made in Italy (best and OE), Spain or USA.