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Still wondering, though, in kg*m^2 is "m" the diameter? This was a wild guess. Initially I thought it would be mass, but kg is the same thing, isn't it?

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Anyway, I appear to be on the right track, because my entities bounce around okay, though they all finish on funny angles because they think they are spheres.

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because of the symmetry of the sphere, each principal moment is the same, so the moment of inertia of the sphere taken about any diameter is I = 2/5mR^2

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The moment of inertia of a sphere of uniform density and radius R is
I = (8/15) * pi * density * R^5

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//moment of inertria, I = 2/5MR^2
     moment_of_inertia = (2/5) *  my.mass* pow(radius,2);
.
.
//distance_from_centre, centre of object to point hit
     vec_diff(temp, my.x, target);
     distance_from_centre = vec_length(temp);
.
.
//Force, velocity * mass
     vec_set(temp, my.velocity);
     vec_scale(temp, my.mass);
     vec_set(force, temp);


//torque = force * distance_from_centre;				
     vec_set(temp, force);
     vec_scale(temp, distance_from_centre);
     vec_set(torque,temp);
.
.
//rot_a = torque/moment_of_inertia				
     if(moment_of_inertia) //don't divide by zero
     {
        rot_a.pan = torque.pan / moment_of_inertia;
        rot_a.tilt = torque.tilt / moment_of_inertia;
        rot_a.roll = torque.roll / moment_of_inertia;
     }
.
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//convert from radians to degrees
     vec_set(temp,rot_a);
     vec_scale(temp, 57.296);
     vec_set(angular_momentum_change,temp);
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//angular_momentum_change = your_angular_formula * sin(theta)
//not confident about this at all, though I knkow sin(180-dot_product) was correct for theta in the linear equation
     vec_scale(angular_momentum_change, sin(180 - dot_product));
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//Now add that to the ship's angular velocity
     ang_add(my.ROT_VELOCITY, angular_momentum_change);	
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				//(moment of inertia) I = kg * m^2
				//moment_of_inertia = my.mass * pow(45,2);
				//whoops this on is for a point mass 
				//moment_of_inertia = (2/5) * MR^2;
				moment_of_inertia = (2/5) * my.mass*   pow(my.diameter/2,2);
				

				
				//distance_from_centre
				vec_diff(distance_from_centre,target,my.x);				
				
				//determin which side of the ship that is
				vec_rotate(distance_from_centre, my.pan);



				//calculate difference in angle
				//between direction traveling and direction facing		
				vec_to_angle(temp2, my.velocity);				
				vec_diff(temp, temp2, my.pan);

	
				

				//local veloctiy
				local_velocity.x = vec_length(my.velocity);
				local_velocity.y = 0;
				local_velocity.z = 0;
				
				vec_rotate(local_velocity, temp);
				

				
				//Force
				vec_set(temp, local_velocity);
				vec_scale(temp, my.mass);
				vec_set(force, temp);
				
				
							
				//torque = force * distance_from_centre;
				
				torque.tilt = force.x * distance_from_centre.z
								 +force.z * distance_from_centre.x;
				torque.pan = force.x * distance_from_centre.y
								+force.y * distance_from_centre.x; 
				torque.roll = force.z * distance_from_centre.y
								 +force.y * distance_from_centre.z;
				

				
				
				//rot. a = torque / I, or
				//torque = I*(rot. a)				
				
				//rot_a = torque/moment_of_inertia
				
				if(moment_of_inertia) //don't divide by zero
				{
					rot_a.pan = (torque.pan / moment_of_inertia);
					rot_a.tilt = (torque.tilt / moment_of_inertia);
					rot_a.roll = (torque.roll / moment_of_inertia);
				}
				
				
				//convert from radians to degrees
				vec_set(temp,rot_a);
				vec_scale(temp, 57.296);
				vec_set(angular_momentum_change,temp);
				

				
				//angular_momentum_change = your_angular_formula * sin(theta)
				vec_scale(angular_momentum_change, sin(180 - dot_product));
				
	
				
				//phew! Now add that to the ship's angular velocity
				ang_add(my.ROT_VELOCITY, angular_momentum_change);