machanical linkage ?

If you want to avoid Hydraulic, go with a cable. Trucks are a bit iffy when it comes to linkage (mainly on off road rigs, but it applies to all trucks). Body flex can cause the linkage to bind up or move on its own.

My '75 D300 has that problem (mechanical linkage) sometimes the body flexing independently from the frame prevents the clutch from working.

My '84 D50 had a similar problem, I had a Challenger/Cuda Slapstik Shifter in it with mechanical linkage. When I'd pull up a hill at an angle (like a driveway) the body would flex separately from the frame and the mechanical linkage followed... Rowing the transmission from Drive to Reverse or Drive to 1st depending on which way the truck twisted. Not fun. I replaced the Slapstik Shifter with a Cable Driven B&M Ratchet Shifter