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I don't remember how much, but you won't go wrong with good ole SAE 30, it's what was expected when the motor was new. 10W-30 probably would not hurt it either if it is cold where you are, or 15W-40 like the diesels use. It's not a high tech machine.
You should be able to find the spark plugs listed in an auto parts store still.
A 534 takes 11 quarts dry 9 to refill and in my book it states
sae 40 +90 degree's and above
sae30 or 20w-40 +32 -90 degree's f
sae20w or 10w30 -10-32 degree's f
sae10w 5w-30 below 0 degree's f