@Jancoe
I'm thinking of something along this general line:
https://images.app.goo.gl/Ft37CEDDecT2YYeU8
The long rails I'm thinking would be made of steel plate, about 4 in high. And either half or 3/4 in thick.
You would back up over the rails end up against the main backhoe frame.
The front end of the frame would have to have grooves where it could engage some pins and still slide forward and backward. For that I'd weld or bolt some kind of ears or shackles under the frame up front. Or even attach something to the snap fast pins.
But you'd back up just far enough to engage the front of the frame in these sliding grooves. Then hook up the hydraulics and push the hoe boom down. Which would have the effect of lifting up the rear axle hooks/shackles.
The more I think about it, the more I think I would build some square cast iron collars that are split in the center and have a hole the same diameter as the outer axle tubes.
So those heavy square collars would be permanently bolted around the axle tubes. And it would spread the load over a larger area of the axle tube itself, and prevent a pinpoint load. And then the hooks that I drew in the picture would actually be heavy horizontal shackles that will slide forward over those square collars.
So push the boom down which will lift the backhoe frame and rear shackles up in the air and once they're the proper height then push the dipper out away from you and that will push the whole subframe and shackles forward to engage those square collars. Then drop in a couple vertical pins to lock the shackles around the collars. And a couple heavy horizontal pins up near the front sliding grooves.
At that point it's tied heavily/firmly to the rear axle. And it's locked parallel with the tractor frame by the front pins. It can jiggle but not move.
I don't think it should be too technically challenging. The hard part is tracking down the 3/4 plate.
For a front weight it's pretty hard to get significant weight under the front axle up there. There's just not a lot of space to put it. If you put it between the front tires, then there's limited volume. That's where a big iron casting would come in handy. But I don't have the wherewithal to do that.
I do have a 400 plus pound front weight bracket that attaches to the snap fast. It's a steel bracket that holds a total of six two inch by 4 inch by 48 inch steel weights in a horizontal fashion as if it's a front bumper. But it sticks out pretty far and I think would be struck by the bucket.
I could sling those weights crosswise under the frame behind the front wheels, essentially where the deck is at now, but being behind the front wheels doesn't do much to counter all that leverage that the hoe has. So I don't think that's workable.
It would be great to attach a smooth 1" piece of plate steel to the bottom face of the loader bucket. The bucket would still be usable, albeit with less lifting capacity. That plate would weigh around 250 lbs and be 5.5 feet from the rear axle. That plus the current weight of the loader structure I think would adequately counterbalance the hoe. Not overkill, but enough.
But it would be a little tricky figuring out how to attach it, and pretty expensive.
For free I could just build some brackets where I could attach my current counterweight pieces. There are six pieces that weigh around 65 lb each. So I could mount two or three of them vertically to each of the outer lower faces of the loader boom. Two each side would probably be plenty. But if not two then surely three would do the trick.
It might look a little janky, but it should work fine, and the hoe wouldn't be installed terribly often.
That leaves the final need to create outriggers. It seems to me that for the cost and the complexity, that winged outriggers give you a lot more bang for your buck, because they spread your load out sideways and make the tractor less tippy to the left and right. I don't think they weigh any extra. And they wouldn't cost any extra to manufacture. So that's probably the direction I will go.
My final concern is the hydraulic reservoir volume. How big is the reservoir on an LBH model?
Bob