A rasp or two can be rather usefull .
just whacking on a square ply plate with a hole in it ,
useing the spinner & a cardboard spacer , to set the gap . ( as in Fitted With the motor in , aligned , to set true )
Then endless refittings of engine !
, a ball pen line around spinner , Fair In with sanding block .
if Yr gunna F/glass cloth it , you need to go a trifle undersize , so it finishes matched .