No replys..
But I managed to add the needed centimeter by welding some spare material to the length, and it came out very good though.
Next is adjusting the length, and make it double.
I will use Litho-plate for this purpose.
This tube is increasing the thrust from 16 to 18 kilos alone. By increasing the turbine to 18, the thrust is well over 20 kilo.
But this is not the first I plan to do, I`ll perhaps take this later.
12 kilos of weight, 18 kilos of thrust, hmmmm, interesting[:-]
Fuelconsumtion is another issue, but making a center-line tank working is no problem.
As I said before, careful on the throttle

Gudmund