I'm not a big fan of chopping up original pieces on the car including the original radio section on the dash bezel for aftermarket. I would just suggest a custom box though. It is made to your liking and is really inexpensive to build. All you need to know is some basic knowledge of how to use a tape and jigsaw. Thus being said all you need is some (2x pre cut sheets)MDF from home depot about $7.50 a sheet. Also I found a local audio store and purchased the speakerbox felt(1 yard is plenty) and carpet adhesive from them. The felt cost $8.00 a yard and the adhesive cost about $4.00 a can. I built the custom box in my fiancee camaro. I will try to post pics of it later. Anyways the box cost me about $27.00 plus my own labor. Also the speaker cut for a 12 will be 11" inches round, the best way is to make a template from a existing box. Hope this helps a little.