The bolts are hardened 10-32 x 4". They have to go from the engine, through the mounts, through the firewall, and through a 1/8" x 1-1/4" ply donut that will be inside the firewall. I prefer the long bolts to having a short one at each end of a threaded aluminum tube. Now if the middle structure (the standoffs) were a solid combined structure then I would go for it. Manufacturers can make a tube stock aluminum standoff REAL cheap, but not one milled from a solid block, and with longer standoffs a solid structure would be much, much better than individual tubes.

The mount material is a hardwood, oak, I believe in this case. It was obtained from the dumpster behind a custom cabinet shop. They throw all kinds of neat wood away. You should see some of the finish grade thin plywood scraps they toss. Usuable size pieces, too!

The primary reason for the forward positioning is to improve efficiency. Placing the prop up against a big round cowl sorta wipes out what the prop is supposed to do at the area against the cowl. Lot's of turbulence between the prop and the engine. Moving it forward an inch or more cleans up the air a little and improves thrust a bit. For the purists, yes, I'm aware that a propeller does not create thrust, but lift relative to the face of the propeller blades.

Secondary reason is that the 2.6 Yak 55 can end up tail heavy real easy. Using a light engine helps make that happen unless you plane for the lighter weight by positioning equipment more forward. In this case the additional forward distance will almost offset the lower engine weight and still look relatively scale. Anyone ever see the propeller of a full scale Yak or Sukhoi up tight against the cowl? They are not.