340 coolant in oil

Only if it were directly under carburetor, if that coolant didn’t come from manifold end port during removal and it appears to have been there a while, dry it up. Look for cracks in the valley and deck relative to that point and check the bottom of the head gasket and cylinder head at that point as well. I won’t say for certain but I believe you are on the right track, check the coolant crossover passages under the manifold as well. I am hoping that it is something as simple as the manifold, I have known of more than one to have had trouble. I know I hate finding cracked decks or cylinder heads...