Model 400 loader

Hello, I recently picked up a model 400 loader that was on a D17 that I would like to install on my D17. After doing some research I found that this loader is the universal fit model 400 and not the model 417 that was designed to fit the D17. The only mounting issue is there is no angle iron brackets going from the mid mount area of the loader frame to the rear axle. They just have the lower cross bar clamped to the mid section of the tractor. I don't think that's strong enough to hold up. I want to build rear brackets like a model 417 loader used. I've seen pictures of them. I can cut out the angle iron and make them. The only thing I need help with is what size the angle iron is supposed to be. It looks like 3" x 3" x 1/2". Would someone be kind enough to measure theirs and reply with the dimensions? Thanks in advance.   
As an interesting side note, the tractor this came off of had a serial number of 10001, which would make it the 10,000th one made, according to what I found on tractordata.   If that's wrong let me know. I was exited for a minute thinking I found D17 #1 but was quickly brought back to earth after finding it had one too many zeros in the serial #.

No difference between 400, 415, 417 loaders - the loaders themselves are all the same, just the mountings are different depending on the tractor it is going on.