View attachment 164731 This is a different thumb for you guys. It's home made as you can see. It opens when I extent the hoe and closes when I retract it. It's not perfect as I loose the normal use of the extenda hoe but it works well and it's sterdy. I can remove it for the times I want to dig deep or don't need a thumb. For those that have never seen a backhoe tow a dump trailer, I load the trailer while it is attached to the tractor and dump it by flipping a latch with the bucket and tipping it back with the hoe. I don't get off the tractor seat for any of this. Don't want to hyjack this tread. Just wanted to show a thumb that can work hydraulicly with an extendable.
I think if you go with your second option, you'll eventually tear something up. You are essentially tying your inner and outer dippers together with the diagonal arm. If you accidently extend the dipper, something is going to give. If you could come up with a really beefy, longer mounting plate that would move the lower pivot point closer to the bucket, it might work. It would be cantilevered out there, so I don't know if you could make it strong enough.