I've never seen an example of your BMW version of 3490. Certainly 3960/3790 Beemer units had a custom cradle which had a wiring harness to connect it to the car's speaker system and perform other functions too. This will be the case if your 3490 version also has that different cradle as catymag has warned above and as i mentioned here:
If it indeed doesn't have a custom cradle but has different hwid to the usual 1376, and you are experienced in firmware modding and further you're confident to proceed without anyone posting to confirm their experience with cross-flashing this unit, my recommendation would be to initially make a hybrid fw from the unit's fw boot.bin and use fw1_resources.bin and fw_all.bin from the standard US/EU fw maintaining the unit's present hwid. If you don't understand any of that then don't do it without asking further.
If you simply want to enable features such as ASR and keep it as a BMW nuvi, then you should proceed as i suggested previously and just attempt to enable features by modding rgn140.
If you need further specific help with either method, post again and we will move these posts to a new or existing thread because either method's OT in here which is for converting 37x0 to 34x0.