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Between my machines, i believe I've got a Tonka and Nylint clamshell i can get pics and measurements on for you. Clamshells need weight to work well.
If you run a Doepke, Tonka, Nylint style clam, and you've got an extra channel to put a servo on, you can attach a calming line to the release hook. Slack the Calming line, drop Hoist, take a bite, raise Hoist, move the load over, pull Calming line to dump. It's not as effective as running a Crowd line as a powered closer, but it works more consistantly than disk and triangle.
I suggest looking into how the real ones operate with lines for Hoist, Closeing, Calming. If you're able to do that it'll work much better than toy style of just hoisting until it hits the opening plate and the triangle kicks the closer hook free.
A patent search is usually good for some drawings you can use as patterns.
Nylint and Tonka have the 'triangle and a plate' to shift the floating hook and dump the bucket
http://www.tnttoytrucks.com/NYCONDiggers.html
Sometimes it even works.
Doepke used calming line release
http://www.tnttoytrucks.com/DPKUnit1.html