I split up some more:

TBaseModel
-TModel
-TRenderModel
--TglModel
-TLoadSaveModel
--TMsaModel
--T3dsModel

The abstract funtions are in TRenderModel and TLoadSaveModel
In TglModel/TMsaModel/T3dsModel i use reintroduce;

Now i can still use:
mesh1:=TModel.Create(nil);
TMsaModel(mesh1).LoadFromFile('models\hog2.txt');

and rendering like:
TglModel(mesh1).Render;

Without a lot of warnings....

Complet Source is for downloat at: http://www.noeska.com/downloads/FrameWork3d-2.zip

Now i need to find out if i can prevent direct usage of TBaseModel but keep shared code there.