Cooper-Horowitz, Inc. recently arranged financing on the following properties: *Hanover Supermarket: 6 Hampton Dr., Londonderry:   A 57,000 s/f shopping center. The loan was for $3.5 million. Robert Vegh represented the firm. * 30 South Main St., Port Chester, N.Y.:  retail center.  The loan was for $3.1 million. Jeffrey Horowitz and Richard Horowitz represented the firm.