Radiator is out, what can I do in the meantime?

Sometimes but not always those deposits you are showing actually come from LACK of USE. Engines sitting for long periods of time or idling often or in heavy traffic deposits accumulate and can't be dissolved or dissipate. Regular maintainence is effective in this area. Also, backflushing the system is equally effective with compressed air. Additives such as water wetters and rust inhibiters work well. A anode stick in the water flow will help. OTR trucks have coolant filters for a reason. Good luck, Tom