Although ZDZ 40 F3A might have enough power for FAI F3A it wont easily pass sound limit. Magne, please run yours side to side test with YS Dingo etc. I believe hard mounted bench test would give enough information is there any sense to start developing softmount.

As we know propeller sound of current electrics is already guite high. With large gas we have loud exhaust too and airframe resonation as well. Intake sound won't be bad because of carb location.