I think it's a very good possibility he is the author of the journals. Think about it, lots of details we have learned about the potential author so far have matched or almost matched McGucket. In the episode "Into the Bunker" Soos found a laptop marked "Property of F" on it, and at the end of the episode "Little Dipper" it was revealed that Old Man McGucket's full name is Fiddleferd H. McGucket. Also, I'm pretty sure you've all noticed the cast that Old Man McGucket always wears on his arm. Well, the author of the journals had six fingers, but maybe they lost one of them somehow which would explain why them wearing a cast the wat Old Man McGguckt wears a cast. That's my thoughts on why McGucket may be the author. If you agree with me, tell me why you agree, and if you disagree then tell me why you disagree and who you think the potential author of the journals is.