Hopefully I'm doing this correctly. I'm wanting to install a pair of 6x9 speakers in the rear of my 86 Monte Carlo. Unfortunately there is 4x10 there now. I'm not wanting to do any cutting, trying to keep as original as possible. Someone suggested a adapter that goes to the undercarriage of the 4x10 and converts to a 6x9. Is this method effective and if so what is this adapter called?