Its looks like Samsung has protected its ROMs and multiloader for this model against cooking.
So now Samsung B7350 is ready for custom ROMs. All you need:
1) nb0 packer/unpacker
2) Hex editor
3) Modified multiloader (without filehash and signature checking)
Edit your cooked custom nb0 with HEX editor to replace last bytes:
As example - your cooked rom nb0 code: nb0.jpg
To nb0 signed with hidden samsung partitions for loader: modified_nb0.png
at adr 0a3d1b84 as for this example you must write adr of signature start as shown on picture (0a3d1af0)
Flash PDA part and any Lang file (Lang file must be present for first boot) with this loader. B7350_Downloader_cracked_for any_custom_roms_v4.2.zip
Good luck in ROM cooking!