If you want one cheap, get a pin on bucket that is a take-off. The dealer is liable to have one of them hanging around in the weeds for scrap price. Take off the pin on ears and weld on a QA plate. It is easy. If I can do it you can do it!.
For the time and the materials most people in the industry would not undertake such a project. I hate to see things go to waste but for about 600 dollars vs the cost of the bucket, fixture to mount to the bucket and the time you are loosing.
I often tell my customers when purchasing a tractor that the 450 dollars when buying the tractor new to have the quick attach is 1,500 dollars they don't have to spend later! You will always get the 450 back at trade time!!!
You are absolutely correct. Most people would not convert a pin on bucket, and I agree 100% you should just order SSQA when you buy the tractor. But so many buyers (including me) don't have the foresight to know that they need SSQA, (I do all I can to tell them) and the lower price of the pin on at initial purchase reigns supreme. But what can I say? I can lead the horses to water, but a lot of them I just can't make them take a drink.