Difference between 545A and D?

[ME83]

I have been looking at different used loaders and have always favored the older Ford industrial loaders. I have found one near me except it is a 545A, while the others I have seen are 545D's. What is the difference between the letters on these tractors? Both are 4wd and from the pics I can't tell any difference. Also, is there anything to look out for with the 545?

Thanks

 

[ME83]

Anyone???

My guess is the A model is an earlier model, but I can't find any info on it. I can find info on the 545D.