Rolf,
You'll want to add a removable motor anchor for the rubber motor.  And then you can use a motor stick to insert the motor through the nose of the fuselage.  To give you an idea what that looks like Here's a link to a video of a fellow master modeler winding his twin motored model.  You'll see the braided motors hanging out the front of the nacelles: click here
You'll notice he is sticking a wire through the rear motor anchor tube as he places the model on the winding stooge.

The motor is held inplace at the rear of the fuselage with an aluminum tube or bamboo shaft approximately 3/32" to 1/8" diameter.  If you look at the various builds in the current builds section you'll see the balsa anchor holes in the fuselage that the tube/bamboo is inserted into through the end loop of the motor. 

The motor is inserted through the nose sometimes with a motor insertion stick and the anchor place through the loop to anchor the rear of the motor.  The motor can be braided or left just as a loop/s of rubber.  (this can be found at Vintage Model Company in England): Click Here
Here's another uk source: Click Here  I haven't personally used either of these sites but hope this is helpful.

Here's a link to the motor loading stick on our site: Motor Loading stick click here

Under the trimming section on our S&T site you'll find some info on trimming your spitfire for flight.
Sky9pilot

Rolf,

You could make the rudder adjustable but most builders would probably not bother at Peanut scale.  Let's see what other's say.  Other methods can be used for effectively changing the angle if you find it's needed during flight trimming: adding a small trim tab, steaming and bending or breathing on it and bending, or adding a gurney flap.  One trick is to use a minimum of solvent based glue to attach the rudder so if needed it can be removed using acetone to dissolve the glue and then remount at a different angle.  I have seldom needed to do so.  I would choose to make the elevator adjustable before worrying about the rudder.

The Spitfire may like having the weight of those blocks forward but I would carve them out as much as possible for lightness and if weight is needed to balance the model for flight would add clay or such as far forward as possible, in the nose block.

Scale elevator - If the actual life sized Spitfire was shrunk down to Peanut size the elevator would be to "scale".  That line on the plan shows how big to make the elevator if you want it to be scale sized.  If you want to fly the model the larger elevator on the plan will fly better.  The model with a scale elevator will be unstable in flight.

Terryman is probably right.  My photoshop rulers gave me deminsions of 1/16"x1/8" spars and dihedral/landing gear brace.  If using the solid wing ribs the hard 1/32" balsa would probably be suficient.  Just me.  I tend to build too heavy.  If you are using the upper tubulator strips I agree 1/32" square would be perfect.

Hi community,
I want to start to build the fuselage but I have a question regarding the ribs. Please see the red circles at rib "G". The slots are smaller than the one on the top of the rib. Which material I have to put in? Is it a strip of 1/32" balsa which joins rib "I", "H"
and "G"? Thx! Rolf

Thank you Ian for the link to the magazine!
The balsa wood I've ordered arrived today. I will start to cut the parts for the wing tonight.
Rolf

Thank you Neal and Mike, your answers are very helpful for me and the things become clearer now. Also the pictures are good for understanding (the plane looks realy good btw.).
Now I'm searching for balsa but I don't know which material thickness I have to order for a model with 13" wingspan. In the plan is described that I need 1/32" for the fillets and the top combing for example. But which thickness do I need for other parts like wings and ribs?
Thank you in advance!
Rolf

Welcome, rollov!  Red outline is of the wing fillet planview...no pattern for such seems to have been provided on plan.  I wouldn't trouble myself with that feature just yet.  The cross refers to the aircraft's longitudinal center of gravity...a proposed balance point necessary for successful flight trimming.  Again...not to be concerned with at this time during your build.  When the model is finished and you're trimming...you can add weight as necessary to achieve balance at that point.

Glad you've joined us!

Neal