Original AM/FM ? (Long Post)

[Ironhorse]

Well after several un-successful swap meet searches I finally picked up an original am/fm unit at the Pate/Texas Motor Speedway swap meet this last weekend. Very nice face plate with minor small marks. True truck am/fm, dial flips easily, push buttons work and has the rear connector. $230, don't know that it works but guy I bought it from says it did when it was pulled and been sitting in the garage for several years. I like the idea of getting it checked out and putting it in the truck to replace the aftermarked am/fm/cassette unit I have. Problem is I also like to listen to cassette and would like cd option. That brings me to where to mount a after market unit and can it be wired to use same speakers as stock unit. I am quite less than knowledgeable about audio wiring so if that is a dumb question, excuse the ignorance there