I have the same style pedestal and am considering a 740. Can you tell me anything about the mount you are using?
It is a mount that I designed a few years ago. Prety simple to build and very "symmetrical" looking for those customers who don't want a gawdy looking pedestal and a giant white box blocking their view.
It often requires a taller pedestal guard so I often use the Nav-Pod SG-10 1" straight guard.
It is simple to build:
*Cut the overall size you want the platform to be out of 1/2" Starboard
*Drill two 1", 1 1/8" or 1 1/4" holes (depending upon your guard diameter) 9.5" on center
*Buy four 316 SS "clamp collars", in the size you need, from McMaster Carr. 1" 316 Collar is part # 9633T19. They make them in 304 but they will rust faster even after polishing.
*Use a buffing wheel on a bench grinder and tripoli compound to polish the clamp collars (they come "mill finish")
*Pick your radius corners and cut them using a flush cut router bit and a template for the radius
*Use a round-over router bit to chamfer the edges for a nice finish.
*Slide the upper clamps on
*Slide the mount board on
*Slide the lower clamps on
*Mount the plotter bracket
*Drill the holes for the wires
*Drill a 1/4" hole in the guard tube
*Use the 1/4" hole as a guide for a Lenox hole saw to make hole bigger
*Use a dremel to smooth hole edges inside and out of the guard leg.
*Buff guard leg around hole with buffing wheel
*Adjust desired height and lock the collars down.
*I also replace the crappy black plastic Edson feet with the newer SS style