I ordered one last week. They would like the 8'' back from the tip of cutting edge all the way across. They will build it and subtract 1/4 '' . They told me two weeks to build. Is the cutting edge worn on your loader? If so you will have to replace it.
There is an opinion of this bar from a guy who had trouble fitting the front part of his bucket with the 8" back measurement. If you have a bucket that the cutting edge or strengthening side strap comes into the inside of the bucket, he advised using the front measurment as he had to grind quite a bit off to fit
I think most B3030 tractors have the 60" bucket so your toothbar inside measurement would be the 58-1/2 figure. That is what I have on my B3030 but I purchased the ATI Toothbar #TBC-7AR from my local dealer.