Beautiful end support. Well done. I have shorter rows at 140’ with just a single post anchoring now. I have cable harpoon anchors and extra posts available, but you have convinced me to use the latter and make an H brace.
I have the Gripple tension devices and they work well. Pull them taught by hand, then use the tool to tighen them fully. Release them like a ratchet strap - tighten them slightly, push the pin tool in to release.