Thanks Neil for your time. Here is what I did:
1-followed the instruction Transform a Nuvi 37xx in a Nuvi 34xx for dummies = Done no problem
2- Run webupdater and upgrade software from 7.10 to 7.50 with others update= everything OK except that I don't have MP3
3-Downloaded the kit from 2xxx and 3xxx series enable features application ( saving the boot bin from the initial nuvi34xx_GCDFile__710.gcd to Ldr.bin and changed the path to garmin/updater/1376. After writing back the altered file reg_140.bin and nuvi off I still didn't get the selected features (MP3, video player, phonelink, custom main menu, supplementary 3D, 2D footprint and Premium Points addressing) I didn't select the others features as I already have them.
I am certainly missing something and as you suggested will double check again the instructions next week ( this week wife needs the gps).
Once again thanks for this community.