Hi Terry, if you haven't done so already try the link below to the Bright supernova page, then in the left hand column you will see Photometry Reference Images. Click on that then pick the galaxy you want ie NGC1620, and you will find a DSS image on which Odd Trondall has noted a number of close stars blue and red mags that are handy to make comparison estimates. If you haven't already try Astrometrica - shareware with a 100 day trial
http://www.astrometrica.at/
Bright Supernova page - an excellent resource for Supernova hunters.
http://www.rochesterastronomy.org/SNIMAGES/
PeterM