I just got one for about $35.00 on ebay for my model 65. It is a solid mount that does not work loose and allows you to see your iron sights. The down side is the optic sits very high and this creates problems. It would be a truly great mount if they would offer it without the ability to see the iron sights and the optic would sit lower. Weaver makes a mount that will clamp in place at the front and bolt in place using your rear sight mount and there are other mounts that will use your existing holes but I think your gun is too old for those. Below is a link to a thread with pictures of the Weaver mount;

Red Dot for a Model 65

The Weaver mount is for K frames but if you check they might make one for N frames.