I'm building a +30 year old Bud Nosen Citabria kit, 105". I have a copy of the plans and instructions but cannot find what the engine thrust angle should be. Anyone know what it is?

The plans show the thrust line and incidence but not the engine thrust angle.

I will be using a 25cc Homelite so will not use the engine mount on the plans. Will mount engine directly to firewall.