If you add maps from nuvi 50 on your nuvi 760, nuvi 760 will not see maps becouse is locked, maps from garmin site is unlocked only for device that you download map.

So if you take maps from your nuvi 50 and if you like to nuvi 760 see this maps, you must first unlock map with this tool:

[Only registered and activated users can see links. ]

Then you add this unlocked map on SD in folder garmin, with name gmapsupp.img or gmapsup1.img, after this your nuvi 760 will see this maps.