Sounds like you have the right idea, but it depends on how you want to use your Volt/Amp gauge. Go to Electronics International's site on this link,
http://www.buy-ei.com/Information/OI...II%20VA-1A.pdf , and look at their installation manual. (Page 9, #3) They give a really good explaination of how to determine which way to install your shunt to be able to read the meter and see the results you want to track. Either in the battery lead or in the alternator lead. You are describing the alternator lead installation, since you are breaking the B lead before the bus in order to install the shunt. You can install the shunt at the end of the B lead or break it and install rings, either side of the firewall.
If the shunt is not marked, the screw on the alternator side of the shunt would be the positive and the one on the bus side would be the negative. They typically have a small + or - stamped on the two terminal blocks. These will need to be hooked up correctly in order for your gauge to work correctly.
Whether it is a separate gauge or a read out on the EFIS, it would be the same, unless AFS specifies something different.
Hope this helps.
Good luck.