Re: Passive voice for think
Well, that's a thought. Not a very likely one, but it *is* possible.
The problem is with the "him" and "you."
I had thought to maybe keep you company -- this is similiar in sound to what you originally wrote. I thought that you might enjoy some companionship before my friend pronounces you dead.
But it's possible that when he says that he will keep "him" company, he means his friend, and the speaker joins his friend in wishing him dead.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.