alphabet.py:
class A(models.Model):
    type = models.CharField(max_length=1, null=True, blank=True)
    a1 = models.CharField(max_length=50)
    a2 = models.CharField(max_length=50)
    a3 = models.CharField(max_length=50)
class AAdmin(admin.ModelAdmin):
    list_display = ('id', 'a1', 'a2', 'a3',)
    
class B(A):
    b1 = models.CharField(max_length=50)
    b2 = models.CharField(max_length=50)
    b3 = models.CharField(max_length=50)
    
class BAdmin(admin.ModelAdmin):
    list_display = ('id', 'a1', 'a2', 'a3', 'b1', 'b2', 'b3',)
    
    def save_model(self, request, obj, form, change): 
        obj.type = B
        
class C(A):
    c1 = models.CharField(max_length=50)
    c2 = models.CharField(max_length=50)
    c3 = models.CharField(max_length=50)
    
class CAdmin(admin.ModelAdmin):
    list_display = ('id', 'a1', 'a2', 'a3', 'c1', 'c2', 'c3',)
    
    def save_model(self, request, obj, form, change): 
        obj.type = C

class A(models.Model):
    type = models.CharField(max_length=1, null=True, blank=True)
    a1 = models.CharField(max_length=50)
    a2 = models.CharField(max_length=50)
    a3 = models.CharField(max_length=50)
    def edt_lnk(self):
        return '<a href="/admin/alphabet/%s/%s">%s</a>' % (self.type, self.id, self.id)
    edt_lnk.allow_tags = True
    edt_lnk.short_description = u'№'
    edt_lnk.admin_order_field = 'id'
class AAdmin(admin.ModelAdmin):
    list_display = ('edt_lnk', 'a1', 'a2', 'a3',)
    def changelist_view(self, request, extra_context=None):
        self.list_display_links = (None,)
        return super(AAdmin, self).changelist_view(request, extra_context=None)