Take another look at the way the stand offs are constructed. There are two "beams" acting as one side of an engine mount. Each beam consists of two "legs" joined by a top and bottom "bridge". Each beam is a solid piece of wood with the central core removed for weight reduction. In this case two pieces of 3/4"x2" hardwood stock laminated together. Beams with considerably more layering are used to bridge long spans and carry heavy loads in home construction. The concrete bridges you drive your car over only have 3 sides, similar to the concept used with the mounts. The fourth side is the ground under the bridge, or in this case the engine and existing. firewall.

Each beam is extremely strong and provides tremendous resistance to twisting loads imposed by engine torque. They also mitigate engine vibration far better than 4 spindly aluminum stand offs. Weight differential is minimal. The upper and lower bridges tie each pair of legs together, and distribute thrust loads over a wide area. Turning the pair of beams (if desired) into a full box mount structure would only require the addition of light ply between the beams, essentially turning the beams into another firewall. There is no need to tie the beams together, making a box (actually a cube at that point) since the engine does that for you.

Another nice feature is the cost. In this case the cost was nothing financially since the wood came from a dumpster behind a cabinet shop. It only needed to be assembled into the desired size and shape. It took a couple hours to size, shape, glue, drill, and thin coat with epoxy to seal the wood. A little time and sweat but no time was spent combing vendor sites looking for the right size, and there was no waiting for the mailman or a delivery charge from the brown truck.

Try looking at a plane thinking about how one part of the plane can addsstrength to another part of a plane without generating excess weight. Composite planes depend on that concept. Much like a tree. Each part flows to the next, with each part lending support to the next section in line. Viewed that way you can build lighter and stronger than the other guy. Every time. In this case the engine becomes the structural tie at the front of the beams. The existing firewall becomes the aft tie. The pair of beams combined with the firewall and engine backplate provides torque resistance for the engine, which is further resisted by the existing firewall and fuselage structure.

Independant metal stand offs are seriously inferior to the mounts used in the photos. All I do is large and larger planes anymore and these mounts will work on any engine.