Rebuilt SD9s

When I was working on BNSF, I had a SD9 which was rebuilt with a modern style cab, modern AAR control stand, 26L brakes, and electronic governor. It also had the modern wider stairs. I had another units which had the same modern style EMD cab, but it still had the original electrical cabinet, can style control stand, and #6 brakes. What is the story on that unit? Why did they go to all the trouble of the chop nose and new cab, but keep the #6? Does anyone know which unit this was?

BN bought eight used SD7/SD9 locomotives in the late 1980's. They were rebuilt at MRL's Livingston shops to be used as power in hump yards like Balmer and Northtown. They were numbered 6240-6247 under BN, and 6140-6147 under BNSF. They were renumbered a few years back, but I'm not sure what numbers they carry now.

I remember that class. When I first hired out, I worked in Cicero. 6246 was the regular hump engine. If it was not available then we got the 2288 (GP38-2) and 442 (sw1000b).
I was wondering about the later rebuilds. These had GP35-peesent style cabs and newer steps. One had a modern control stand and electrical cabinet. The other had the external changes, but still had the original electrical cabinet and can control stand with #6 brakes.