Glad I could help!

Now that we have a possible explanation for the vertical mark being left of center, I highly recommend we check the horizontal mark before we drill the holes and install the blind nuts to mount the engine mount to the firewall.

Fit the cowling to the fuselage to where it "looks right". i.e. not tilted up or down, but "flows" with the lines of the fuselage. Then using something to measure with such as a metric tape or a balsa stick, measure the depth from the face of the firewall out to the front of the cowling, and depending on what spinner you are going to use, you'll need to add a bit more to that measurement, as some spinners have a flat back plate while others extend rearward behind the face of the prop drive. You'll also want to add a bit for clearence between the spinner and the cowl.

Use your measurements to locate the engine on the mount fore and aft. Drill the mount(s) and then fasten the engine to the mounts. Now we will confirm the horizontal line.....

With the cowling removed, and the fuselage held in an upright position, place the engine and engine mount assembly on top of the firewall where the marks are, then still holding the fuselage upright fit the cowl. Does the center of the crankshaft fit the center of the cowl opening? If not, then you'll have to move the engine up and down a bit (that would be horizontally since you are holding the fuselage upright) to get the proper fit, again, with the cowling in place so it looks right.

Rube