On my 1998 1800, it's 34'' from the top of the bow to the waterline. I have a Motorguide iX5 60'' shaft mounted on my bow, and I usually run it with the shaft as deep as I can get it. In 1-2 ft seas, the trolling motor prop will break the surface of the water. It's fine if its 1ft seas or less.
I would NOT want a 54'' shaft. The prop on my motor is 10.25 inch diameter, so with one of the blades pointing up, it's 5.125'' up the shaft. The blade tip really should be at least a few inches below the surface if its calm, more if it's rough. My motor base is 7'' tall and the shaft depth control collar is 1'' tall.
Lets say you're running a 10.25'' prop with the prop tip 6'' under calm water. That's about a 5'' prop radius + 6'' underwater depth +7'' motor base height + 1'' collar + 34'' bow to waterline =53''. That'll give you ONE inch to spare. I don't think it'll work, any amount of waves at all would make the prop break the surface of the water.
My 34'' measurement was done with the boat empty and tied to the dock. If you have 2 guys standing at the back fishing, your bow will likely be an few inches higher?
My 60'' is as short as I'd go. I'd even go longer if you'll regularly use the trolling motor in rough seas.