Get it running, see how it starts,stops and runs, do a compression check.

If you're getting it for the engine then whether it's viable or not should be your focus.

That dark coolant may suggest well rusted internals due to marinating in coolant which long ago lost its rust inhibiting properties.

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'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.