finally we ended up machininig the fan so it can fit an earlier 911 housing
so we had to machine the alternator mounting , since the fan is wider , and decrease the fanīs diameter , also the hub had to be modified so it will accept the old key.
the good thing is that we can switch between fans on the same housing since all of them will fit
in the future we will dyno the 5 blade vs the 11 blade vs the 12 blade fans !! and we will post the results