Regardless of the bolt size, it is "rubber" mount you are torquing,
not the bolt, whether Lords or others.

Wrong.  Using engines of at least the 320 size with a dynafocal arrangement, the "isolator" is to become a rigid part of the motor itself.  I.E. The bolt thru a washer with rubber, thru a heavy steel bushing with rubber wings, thru the rubber, thru a washer, thru the engine and all bolted up as a rigid body with ultimate load (for the upper bolts, 9 G's in my Lancair) carried by the bolt.  This is a bolt in tension.  The purpose of torqueing is to pre-load the bolt so that it experiences no loads greater than the pre-load it was designed for and thus is not subject to "stretching."  The bolt is also sized for this purpose.

 

Finally, the rubber sandwich concoction (held by the rigid buildup) supports the whole mess on the engine mount and absorbs a great deal of vibration.  Rubber composition varies from hard (little movement,small 1G sag, some transmission of vibration) to soft (more movement, more 1G sag, little transmission of vibration).  Remember that the length of the bushing and the weight of the engine controls the static 1G compression of the rubber in the mount, not the torque on the bolt. 

 

I hope everyone has torqued the engine mount to firewall bolts at the bolt rated value.  Furthermore, I hope everyone checks that torque at every annual condition inspection.  If, thru the miracle and history of glass movement, those bolts "loosen" then an additional vibration load is being transferred to the airframe.

 

Also, a quick check thru Google pointed to an RV reference table, look down at the bottom for the Lord mount reference.