im very satisfied with that answer! But my problem is that the firewall is fairly weak so i only got one shot to drill the mounting holes at the right place. If i drill the holes in the wrong spot, then i cant "re drill" because that will probably make the firewall too frigile.. []

If the holes are drilled in the wrong spot, the prop. wont center in the cowl because the holes are drilled in too far or too close to the firewall centerline...

1.5degres down and 1.5degre right thrust:

drill holes, cm from firewall centerline = "root out of" ((12.5^2)-(12.5sin 1,5)^2) = 0,88cm


Is 1.5deegres a good start? Perhaps i can do the firewall holes slightly larger then the bolts so that i can adjust the a bit if nessesery...