Hi!
Getting the silencer more outward is simple! Just fit a spacer ...let´s say 8mm thick of aluminum between the silencer and the engine.
Make it yourself by sawing, drilling and filing...have done this myself on several engines...works fine. Just get longer Allen bolts for the silencer!
As for props try a 11x8 or a 11x9 APC I would not try a 3-blade prop as most of the time they are inferior to 2-blade props performance-wise and as loud or louder.
APC props is regarded amongst fliers around the world to be the most silent prop available on the market. MA props are about the lousiest, loudest, with worst performance props you can get your hands on... Why do you think competitors mostly use APC?!

As for silencer Is it a doubble chamber silencer you have ?

Regards!
Jan K
Sweden