I was reading some old posts on another forum about if you de-turboed a SD60 to make an SD58 like they are doing with SD40-2s to make ersatz SD38-2s for yard service.
So I found a drawing of a SD50 and converted it to my version of a SD48, since the SD50 and SD60 look almost identical.
http://clcotrains.embarqspace.com/#/rebuilds/4525844461
I removed the dynamic brakes, 1 cooling fan, put in paper air filters (I think that is what it is) and put on new exhaust stacks.