Do you really want to build the BH yourself?
Don't know if Deere makes subframe mount BHs anymore. My subframe BH is JD, but is not a current model and is not designed for my tractor. I had access to it at the JD dealer for taking measurements. I welded and cut the subframe, and made brackets to fit my tractor.
I am pleased with the result, but that was enough work for me. That was 3 or 4 years ago. Everything is holding up so far.
Adapting an existing subframe BH to your tractor is just an option that you may not have considered. A JD #7 BH is a subframe model that might be adaptable to your tractor. They aren't in production anymore, but your dealer could do a search and see if one is sitting around somewhere at another dealership. Even a NH or Kubota model might work just fine. You would almost have to see it first, measure the critical dimentions, then decide if the project is feasible. It might very well be easier than building the whole thing from scratch.
OkieG
