I don't use 4x5, so just guessing here... 1/200th of a second at f/45 will need rather a lot of light. Also, might you have to consider the bellows factor, in terms of the light you'll need to make a decent exposure.

I wonder if maybe a shot in daylight would be a good idea, at least then you can rule out any flash sync issues?

Like I say, I don't shoot 4x5, but I'm interested in trying, so your progress interests me.