gumhead,
The manual isn't much help. There is only a single paragraph about Installing the Engine Mounts and it basically says nothing everyone wouldn't know already. There is a small picture showing the motor mount centered around the hole. That's NOT where it ought to be if you want the prop to be centered in the cowl. The picture also shows the mount arranged with the engine pointing down at 225 degrees. That puts the muffler for the 4stroke they picture elsewhere down in the hole at the bottom of the firewall. They say to drill four 5mm holes for the engine mount, and to make "sure to space the engine mounts to fit the engine you are using." That is pretty much all they say in the paragraph.

In the Installing the Throttle Pushrod Housing section that follows the Installing the Engine Mounts section, they say that "The distance from the firewall to the front of the engine thrust washer should 4-3/4" (121mm)" (that's EXACTLY how they printed it)

Since you fit the cowling later in the assembly, the distance is not critical for that. Matter of fact, the cowl has a lot of leeway front to back. I chose to install mine probably 1/2" back from where their cowl seems to be in their pictures. Their pictures show the front of their cowl probably 1/4" behind the back of the prop drive washer. Their pictures also show a cowl that has a lot more cowl up front. Their front part extends farther into the hole and makes a lot narrower hole than mine.

If you use that hole as a centering point for your motor mount, you also could have problems with the tank being too high. I mounted my motor at 270degrees for a couple of reasons. Turned out the tank wouldn't be too high that way. And I used a Pitts muffler and I wanted the tubes to stick straight out the bottom. As I mentioned in other posts about this mount installation, the hole is correctly located for the right thrust so the left-to-right location of that hole is useful for lining up the mount. But the hole is located for upthrust, and the firewall has downthrust, so I moved the mount location straight up the amount the hole is missplaced downward.

Hope this provides what you need to know and the other stuff helps.