Follow-up:
I finally had removed my sunsport seating. Did not take many pictures, but here is a picture with the seating removed. Feels like a different boat with all that floor space!

The procedure for removal was as follows:
1. Remove "Futon" section of seat bottom and back by removing the four 1/4-20 bolts that are in the sliding slots.
2a. Unscrew the "Headrest" section from the gunnels by removing screws from under gunnels. Mine only had 1 at each end, but there were holes for 3 at each end. Requires stubby screw driver (phillips) and a mirror helps.
2b. Unscrew the "Headrest" section from the starboard support box by removing 3 #10 nuts and washers from the studs that stick down into the engine compartment.
2c. Lift out the headrest section
3. Remove the Starboard support box by removing 6 screws from the floor. No other dis-assembly of this box was necessary, as two people can lift it out in one piece.
That's all. Now that I know how, two people could do this removal in about 1/2 hour. Replacement also 1/2 hour for 2 people. So I'm sure I will do it again when I need good access to the engine.
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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings