BN 1798 never existed as GN 725 was wrecked and retired in 1969.
The GN 725 was built in December 1957 using parts from GN FTB 251B. It was delivered in the Classic Empire Builder scheme. A photo of it is shown here on Pinterest:
The GN 725 was later painted into GN's simplified orange and green scheme.
It was wrecked at Marysville, WA 6/6/1969 while leading a southbound road freight after striking a GN local stopped on the main line. The 725 was scrapped 8/15/1969.
After the BN merger the GN 725 was to have been renumbered BN 1798 but that number slot was left open and never used.