As Henry mentioned, it is unnecessarily tall. This will result in loss of stability - it may suddenly fall to one side, together with precious kayak, when you hit some bump or just sway a little on soft soil.
I thought that I could just lay kayak over it while the cart is on it's side. I would then lift up the cart and sort of push/slide it under the kayak until I reach the point where it's basically centered, and apply the straps.
Ok, but what you’re going to do when you pull the kayak ashore, with half of the hull still on water? Laying it over to one side wouldn’t be a good idea then. And there is no need. Kickstand is easy to make. Tie short pieces of ½” tubing or some wooden sticks if this is easier, to the ends of horizontal T-legs. I’ve done this on my cart
http://www.geocities.com/alexm221100/cart.html (the end of 1/8” OD brown line can be seen on one of the photos). You may get away with one kickstand only (i.e. on one T-leg only), but 2 will work better. My cart has only one lateral axle (yours has 2), so each T-leg on my cart must have its own kickstand. While having 2 kickstands might look inconvenient, in practice it is not. They naturally find the ground, you only have to touch them a little to correct their position. They must be short enough to keep the horizontal tubes at approximately 30-40 degrees. Then, when you load the kayak on and level it up parallel to the ground, the kickstands will just dangle, not reaching the ground.
As Dave mentioned, there are many good ideas implementing PVC pipes and joints. If you look at the original drawing by A. Ferguson shown in the link above, it suggests joining 1” aluminum tubes by either PVC Tees or by welding the aluminum. I took it to welder, because wanted it to be very heavy-duty. And heavy-duty it is. I can carry over 200 lbs on this cart without much efforts, either in “kayak” or “luggage” mode. Another reason to weld, rather than use PVC joints, was that I wanted to have as fewer separate parts as possible, because I'm using it in wilderness trips and don't want to look around for parts and assemble them in inclement weather and/or unprotected shore, when I need to get away from the shoreline fast. Welded T-legs, joined together by hammock straps, are essentially "one" part, and it is compact - 12" x 7" (compact cart frame is invaluable in narrow kayaks like Kahuna, K1 or Cooper, in multiday trips). The only other part of the cart frame is narrow stainless axle - it doesn't take any room in a kayak. For daytrips you can afford less compact frame, of course.
