My first 4x5 was a Cambo. Short of finding the actual Cambo clamp for the square monorail - a fast and inexpensive "fix" is to drill and tap a 1/4-20 thread in the bottom of the rail on one or multiple places near the middle of the rail length. You then just attach it directly to any tripod.
For architectural work, stay away from ball-heads. You need separate and easily adjustable forward and lateral adjustments.
Lens: It's hard to imagine a good architecture lens kit without a 90mm - but a "bag" bellows is pretty important for getting the most out such a short focal length. Keep an eye out for a good used 120/121mm lens.