Doug:
you are correct that there is an equal force going up as there is down, all of the forces are contained between the head and the main brgs, at least as far as the up/down vector.
or rather i should say the vast majority of those forces,
the only things transmitted outside the block are
1. torque action
2. imbalance issue's with the engine
3. sound, vibration of ignition
also it is good to note that in 99.999% of concrete mounts they are still resilient as the ground has some give, some ground obviously has more give (damp clay)
if there were any real down force's they would abraid or work the concrete to death at the mount points.
my contension is basically if we had a steel ball, with a shaft welded on it
and cast the shaft into a concrete block and then set off a bomb withing the steel ball we would not have a very large down force if at all,
but we would transmit sound, noise or whatever you want to call it. certainly not a 600lb hammer blow
the mounts i referenced to are common mounts used for all sorts of hd truck engine's, most everyone uses them, are as common as dirt.
they last forever in very hostile environments, and handle torques in excess of 50 times that of a 6/1 comfortably.
with the diagram example i was only trying to illustrate how to limit the one component that is common to all engine's, that be torque and anti torque actions
we can limit that rocking action by simple design, leaving us with only
the up/down, and the side to side action
these rubber mounts are very dense, and only about 3/4" thick when torqued, the shear strength is such that the engine likely will not move fore and aft, or side to side but very little, leaving only the up and down component, which is very small in a well balanced engine to start with
the up/down, side to side, and fore/aft movement are far smaller components than that of the rocking component due to torque and antitorque action.
the up/down is going to be the sound transmission plane, so balanceing the engine should be done first to reduce what needs to be mitigated, whats left the rubber mounts will isolate quite well.
good mounts on a cat, cummings or whatever do a really nice job of isolating the noise/sound from the engine to the cab, but when one does wear out and fall out, the engines will damn sure rattle your teeth out.
if anything the truck mounts might be too stiff, and as such not isolate as well as a softer mount.
just like everything else in life, it is a comprimise. less movement more transmission, more movement better isolation.
i like the truck mounts because i can torque the thru bolt to fine tune to an acceptable comprimise between little movement and good isolation.
i still say that eliminating the rocking components effect on the crank/flywheel/brgs, is a huge step in the right direction
bob g