Recommended bolt torques are usually based on the yield strength of the bolt material which is why SAE Grade 8 bolts have a higher recommended torque than SAE Grade 5 bolts. SAE does not have a classification higher than Grade 8, but most socket head cap screws have a higher material yield strength than SAE Grade 8, so they can be installed with a higher torque, and the socket head cap screw manufacturers will list this torque in their literature.
If installed as a cap screw, then the installation torque may depend on the material it is screwed into as the limiting factor may be the shear stress of the female thread rather than the shear stress of the bolt body.
If I understand correctly these cap screws go into a female threaded aluminum housing. Therefore I would go with the Lycoming specified torque value for the fastener.