Voltage Regulator Question / Pertronix

Hi all! Got some questions about the voltage regulator. Two days ago I built in a PERTRONIX Ignitor 1 upgrade, bypassing the ballast resistor as described. Everything works well so far. I only noticed that my dashes amperemeter needle is not standing at one position anymore. It seems to bounce to the left and the right. Did I forget to change other things in relation to the Pertronix upgrade? I got a stock alternator. I read that it is usefull to change the voltage regulator? What are your opinions? Will this replacement be any good?
http://www.autozone.com/autozone/parts/_/N-9ci9t?checkfit=true&counter=0&filterByKeyWord=vr706&fromString=search&isSearchByPartNumber=true&itemIdentifier=129965_0

or this one? http://cgi.ebay.com/ebaymotors/Mopa...tZVintageQ5fCarQ5fTruckQ5fPartsQ5fAccessories

I added a pic of my engine compartment. What is that small can element, connected to the regulator? I didnt find it in the US service manual. Any ideas?