not wishing to spoil the party so to speak, but consider this, a funeral is not about you, it's a show of respect for the dearly departed and the family and friends they left behind.
In Scotland it's not the norm to wear the kilt to a funeral, unless the deceased themselves either wore a kilt, loved the tartan or was highly patriotic.
I would personally consider every aspect, did your friends father admire your wearing of the kilt, if so wear it for that reason, if on the other hand he never saw you wearing the kilt, then perhaps on this one occassion wear clothing that will fit in with the rest of the mourners.
or put simply, do you really want to stand out amongst the crowd and steal the centre of attention at this sad occassion.
Perhaps ask the approval of your friend ?

Chris