RE: trust the thrust line?
I just went out and drew up a way to measure how much offset to the left you would need to center the engine in a cowl. Because it's a jug it isn't that important, it's big and opened. I just draw a straight line then measure the degrees of the thrust, in this case I did it at 3 degrees. Drew another line to the 3 degree mark. Then I just measure how far out the front of the thrust washer would be when mounted and measure the distance between the lines and that tells me how far over to the left the engine would need to be moved to have the shaft centered.
When I build a plane from plans I put no thrust in the engine or fire wall at all if it doesn't call for it. Then I test fly the plane to see what it does without any thrust. Usually pulls to the left on the up line a little. Using washers behind the left side of the mount I start adding one washer at a time and keep flying until the plane doesn't pull at all. When I get home I make up a shim to go behind the mount that gives me the thrust required. If any! Depending on the type of plane I may plug the mount holes and move the engine over so it is centered in the cowl. This is important on planes like an Extra that has a cowl with a smaller hole in the center. On something like a Sukhoi I don't bother because the cowl is open like on your jug.
Some planes require thrust and some don't. I never know unless it is stated in the instructions or after I have done the trim flights?
I'm building a small Ultimate right now and it has built in down thrust on the fire wall so the designer of this kit discovered the need for it during his testing.
If it doesn't call for thrust and the fire wall doesn't have it built in I wouldn't worry about it until after I have done my trim flights.
The worst thing that will happen without the thrust will be the plane pulling either up or to the left. Your plane will probably pull a bit left, my Bipe would probably be pulling up so it was built in.
If it doesn't call for it in the instructions I wouldn't worry a lot about it.