1. Do you feel the Sidekicks are secure enough with only one fastener attachng to the tracks? Ultimate test: Can you tip the kayak on its side on dry land with the sidekick on? (test only. This would be very bad practice though I imagine there could be shallow water scenario on a flipped kayak that someone could invent)
I find it to be very secure for ocean fishing and standing on the flats, one bolt seems to be more than enough. However, Revo makes a good point about the added stresses when sailing. I am not sure what the tolerance is on the plastic but I will discuss this with the folks at YakAttack. The current tab is only about 2.5-3" long. I would not think adding a MightyBolt to both sides would be a tooling issue (but certainly a cost issue) and the GT90s come in 4", 8" 12", and 16" lengths so there should not be an issue mounting more than a Sidekick and a Screwball.
Keep in mind that the GT90s have a threaded backing plate that runs the full length of the track so you could not ask for a more secure attachment to the kayak.
2. Is that adaptor mount block made for the Sidekick with holes and embedded locknuts in it or is it just a block that must be drilled to attach the saddles?
The block has Nyloc nuts embedded and all you need is a Phillips head screwdriver. I think thumbscrews would be a nice upgrade.
3. Does the saddle mounting block have to be mounted at the end of the track or can it slide anywhere along the track?
It can be mounted anywhere on any GearTrack and it is a breeze to adjust. You can slide them up and down the track (loosen bracket first) and pop them on and off with ease. I just mounted it on the end because the location suited my purpose. I also have GT90s on my Adventure and Oasis and I plan to snap the Sidekicks from kayak to kayak. It's also nice to not have the pole on the kayak when I am not using the Sidekicks.
4 Does that adaptor block have a Yakattack part number and what is the cost?
I believe they are calling it the GTAB and I don't know what the cost will be. I would contact YakAtack.US for more info on that.
Great answer. I think I will be going with an 8" GT90 tracks behind the seat and a 12" GT90's up front like you did. I will be using the fullback backing plates even in areas where I can reach. I hope the floatation blocks don't get in the way in the back. I am not concerned about the "plastic" tab. That plastic is plenty strong enough for my kayak rod holders and downriggers as well as the mounting plates on my electric downriggers with 15 lb lead balls on my big boat. Think positive. If the Sidekick comes off, at least I won't lose it. It floats!
BTW, I bet the "Mark II" model of that GTAB plate will span both sides of the Sidekick saddle mount and have arced slots to adjust to keep saddles parallel on non-parallel GT90 track pairs. Yakattack is a very sharp company. If they do that, I hope they keep the single mount so folks can maximize track space like you did.