I believe the carbs on the .12 engine will fit on the small block .15 engines (NS15 S5) and vice versa. Just that the 10608 carb on the NS15 S5 engine is without the 3rd brass needle screw which is similar to the one that the JP FX engines have...

BTW, a 3 port engine will fit a 5 port sleeve and vice versa regardless of it being a Novarossi engine or a JP FX engine...