I have a 45W with hydraulic dump, and over time have had several 45, trip-type loaders.
Depending on the welding, that can be serious or not. It depends on the quality and location. You'll just have to judge that one. I've had to grind off some terrible welding, and cut some tubing and replace sections. If done correctly by a good welder, it can look like factory.
Finding all the correct mounting parts is important, and I really think they almost equal half of the loader value. But that means the two axle mounts, the two bracing pipes, AND all the nuts and the two forward plates that accept the pipe ends. It is no fun to have to fabricate loader mounts !
You didn't say what year of 'B'. If you have a later model row-crop style tractor, and the loader came off of a similar styled '60', and all the brackets are there, it should bolt right up.
Remember, a loader on a 'B' is not fun compared to having it on a tractor with live hydraulics and power steering, but it will lift quite a bit.
I just rememeber the day we took the 45 off of the 'A' and put it on the 70....you could actually raise it when you were sitting still !
70D // 855