How to replace internal BB with external BB on belt drive bike?

My Rohloff touring bike has an internal bottom bracket (BB). I would like to replace this with an external BB.

Current components

1. Front Sprocket: Gates Carbon Drive, CDX, 4 bolt 104mm BCD, 50 teeth
2. Cranks: Truvativ SRAM K28JAN21 / 175mm
3. Internal bottom bracket: Shimano BB UN300, 127 mm length, casing width 68 mm
4. Belt: Gates Carbon, CDX CenterTrack, 120T CDX, Part number = 11M-120T-12CTS BLACK, Belt Length: 1320, Tooth Count: 120, Pitch: 11"

I want to replace

1. 2x Cranks (blue)
2. Internal bottom bracket (green)

I want to keep

1. Front sprocket (red)

New components

1. 2x Cranks
2. External bottom bracket

In pictures:

Questions

1. Is it technically possible to replace the internal BB with an external BB?

1.1. The front sprocket and the rear sprocket need to align so that the belt is not bent.

1.2. The installation should be simple, e.g. no adding washers and other hacks to get the 2 sprockets to align.

2. Because of costs I would like to go with Shimano parts (hollowtech2).

2.1. Would this be possible?

2.2. What other manufacturers are available?