Coolant Flush Question

On a 96 Roadmaster wagon are there two knock sensors (one on each side) that double as block drain plugs or is there one KS and one actual drain plug?

actually the shop manual says both knock sensors are drains. I hate breaking things and put in a prestolite flush kit hooked up to the heater hose. then after circulating flush through the system 2 days I warmed it up with cap off reservior tank and then when ready to flush, cracked/opened radiator drain replacing coolant with water from hose. I continued to run, radiator cap off, hose on medium, regulating level with the radiator drain plug. Once I was sure it was totally flushed, I turned off hose , radiator drain and engine and let it cool. once cool, I drained the radiator fully and closed, water off.
Now is a great time to replace thermostat and radiator drain plug. Then I added 1/2 of total capacity in 100 percent coolant. Mixing 50/50 there is no way to allow for water still in engine. Then top off with fresh water.

Thanks! I wasn't sure if I should buy one or two knock sensors. I just want to be prepared if they break.