which cylinder cowl for Polini 115?

Hello from New Zealand

the small door 50 cowl wont fit at all,  and standard 50 cowl goes over but is too tight on the polini 115... (50s cases.)

The fan holes of the 50 cowl line up,however the polini115  fins touch the plastic and the screw hole on the wheel side is way off and leaves a finger size gap

Is  SIP part 15073900 what I need to get?