For now, the flight numbering scheme after the res cutover goes something like this for international/transoceanic routes:

DL001-299 are all the TPAC (and interport) and TATL flights, together with some random 600+ series flight numbers for some TPAC services.

DL001 - DL229 are pretty much all routes that use pre-merger DL equipment (777, 767, 75E) regardless of whether it was a pre-merger DL or NW route:

Examples:
DL1 JFK-LHR 764 (pre-merger DL route)
DL18 PVG-DTW 777 (pre-merger NW route)
DL70 NRT-PDX 763 (pre-merger NW route)
DL97 GUM-NRT 763 (pre-merger NW route)

DL230 - DL299 and the DL630-DL650 range are routes that use pre-merger NW equipment (744, A330, 75A).
Examples:
DL242 DTW-AMS A333 (pre-merger NW route)
DL281 ATL-NRT 744 (pre-merger DL route)

When the equipment switches, the flight number will also change: E.g.,

NRT-SFO (pre-merger NW route)
Currently an A332, so flight number is DL 634
Switches to a 763ER starting June 1, so flight number becomes DL172

JFK-FCO (pre-merger DL route)
Currently a 763ER, so flight number is DL 148
Switches to an A333 for summer, flight number changes to DL 246