He looked around and saw an all manner of contraptions nailed to the wall.
This particular usage doesn't make sense.
A possible way of using it in a similar way—although not one I've ever actually seen—would be as a compound adjective:
He looked around and saw an all-manner contraption nailed to the wall.
This might "work" (or at least be understood) in the same sense that an all-purpose contraption works.
However, all manner of is actually an idiom, and would not normally be used differently than in its usual way as defined by Merriam-Webster:
: all kinds or sorts of (things or people) • The store sells all manner of musical instruments. • All manner of people come to the city.