Ouch!!! Ability only comes with knowledge and of course practice no one person is born with either. Ability to read between the questioner's lines is an ability a lot of folks have here. Now for a little free knowledge, to file internal curves you will require a set of double ended "Riflers files" to get into those hard to get curvy places.
I have long ago come to the conclusion that keeping knowledge and taking it to your grave without passing it on is doing this world a disservice. We have lost enough knowledge from the past, I am sure all my apprentices would whole heartily agree because I filled their heads with it until it hurt, making each well rounded and knowledgeable Engineer.
Finally an aftermarket accessory will never have the looks of a factory made and fitted item, I am sure many care owners will vouch for that, but if you really want that item there is nothing wrong with the next best thing.
