The SVRy snow plow #1 (there were 2) really fascinates me also. I haven't tried to do a study of the photos of it, but I think it sorta evolved over the years. Besides being a wedge plow as you stated with flanger blade, it was sort of a home grown Jordon spreader with wings as well. It would be interesting to know if they had the ability to power raise and lower them as well as forward and back. I'd assume air was used. Being a person that enjoys the comfort of a warm stove in winter, I have wondered if the cabin on the plow was heated. If not it must have been one cold SOB. in the dead of winter and bucking 15' drifts as has been reported. I don't have the car rosters in front of me, but I recall under MOW equipment it lists a #2 plow that was built in the early 40's using a wedge plow blade from a Caterpillar #12 grader mounted to a flat car if memory serves me. Someone told me that a snow plow was left in the S.Baker yard long after operation ceased and it was later cut up. Not sure which one. Anyway one thing I had been curious of was whether they ever plowed snow with 250/251. The fact that they built a plow in the 40's is a pretty good indication that they did.
I believe the plow was stationed at Austin at the time of the stuck trains on Larch, which probably makes sense as it is closer to all of the summits than S.Baker, but there is a photo I think in R.S.&P of the plow in front of 50 pulling the daily pass. train westbound near McEwen, so the evidently started out with it on that end of the line. I wonder why SVRy never used pilot plows on the engines (or did they)? At least 4 engines had Priest flangers, but there aren't many photos taken of winter ops, so theoreticlly they could have.