After putting up with NO turnbuckles and just fixed chains and a solid bar to stabilize the lower links on the Massey 245 3 point, turnbuckles are an improvement.
Kubota is now using a wonderful square tubing inside square tubing with a drop in pin on some tractors. I would think you could fabricate one with a little effort, but the last time I tried to build something for a 3 point out of spare parts, it got too expensive too quick.