Just Bought a new boat and I do not like the factory unit (Hummingbird PM 170) In-dash. looking to change out with a better unit. I am going to try to keep from drilling but may end up doing so. Would love to find a gps unit that will fit in the same dash mount. I am looking at Lowrance M68c/Map. So far this is the only one I have found that can be mounted in the dash. Any ideas will be greatly appreciated.

I had the same issue awhile back and was looking at the M68C.   I decided to go with the LMS 520C just because I wanted the bigger screen for viewing both the map and the graph in split screen mode when looking at off-shore structure and cover.

The draw back is you'd have to gimble mount it next to the console on the gunnel instead of in the dash.  But I think the bigger screen is worth it JMO.

Thanks. I will take a look at the 520 and the gimble mount.