On chain sizes...

Acco has a chart listing all the measurements of various sizes of chain, so you could use that to see what you have. It's here, and the chart is on page 4.

http://www.peerlesschain.com/downloads/PeerlessAcco08.pdf

Also, it is often marked on the chain links. Either "3B" or etc.

BBB has visibly shorter links (of course if you don't have other chain to compare to, that's not really helpful), whereas to me, G3 (proof coil) and G4 (high test) look about the same.

Here is a Lofrans chart of gipsy sizes. I don't know that these groupings are always exactly the same for every manufacturer, but this gives you the idea:

http://www.imtra.com/downloadTypes/Lofrans_chainwheel_chart.pdf