Many of the 3 point mixers currently available require a hydraulic top link to accomplish the dumping action. Back in the 60's and 70's there was one called a TransMix that used just the lower lift arms to do it's thing.
If you find one, buy it. They work great. The company has been out of business for a long time.
Here's a crude website containing all my mixer pics for anyone needing help figuring out how a TransMix mixer mounts on a tractor. Be sure to read the photo captions (separated document).
Look at photo 18 and 23 to see the mixer at rest and in dumping mode.