Don't worry about the extra weight. You will not notice it at all. When I built mine, I even emailed Goldberg because I wasn't too sure. They said it is fine. It flies very well with that weight added, but I cut an extra hatch under where the fuel tank goes, and installed the battery up in front of the landing gear, but behind the firewall in the space under the fuel tank. A 12 oz. tank gives plenty of flight time.
Dick - The Venture looks like it might be a nice build. The price doesn't look bad. I guess it's a question right now of whether you'd rather be flying or building right about now. Have you looked in the Pattern forums to see what planes those guys are talking about?
http://www.btemodels.com/venture.html