Dick, to go back to an earlier question of yours, I dont know the Bradco 9HD, so I dont know whether Kubota used it.
I have seen the 509 and 609 on the 3710. For some reason the 609 looks bigger to me. Almost too big. The 611 must look gigantic. I like the 509 on the 3710. I was quoted roughly $7600 installed for the 509. I believe the 408 is a better fit for the 3010. I was hoping to put a 408 on my 2910, but they dont make frame brackets for the B series.
In fact, I was sitting on a 3710 with a 509 the other day. It must have had the frame extension kit, because the toolbox was usable and hoe seat didnt touch the tractor seat. I think this is the best fit I've seen on the 3710. The only problem is that if you sat straight up, you would bump your head on the folding ROPS. (And I am only 5'10".) This wasnt bad, because you sort of naturally slump sitting there, and I didnt hit when slumped. It may be worth considering the short nonfolding ROPS or the tall hoe ROPS.