I know this ended already, but what set(s) is the HVO-7 for?
Seemed reasonable enough:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&_trksid=p4340.l2557&rt=nc&nma=true&item=310306185320&si=pGeVyxrK8%252BoGT1zIqSJmaDvxSwU%253D&viewitem=&sspagename=STRK%3AMEWAX%3AIT

According to their 1951 catalog it's for 7" - 22" sets and equivalent to a GE77J1.