Look around on tocmp.com they might have a diagram. As for the radio, can't help you there.
There are a few places that convert the old to new inside so they look stock. Price is probably up there though. Here's a couple places.
I just hung my radio off the bottom of the dash and left the original working in its original place. Putting any kind of aftermarket radio in the factory place is nearly impossible unless you are willing to cut up your gauge area. If you dont want to hang an aftermarket radio off the bottom of the dash, you can always hit up a junkyard for a factory center console you can put under the dash that accepts a radio. They do make radios that will fit in the factory location but most have tape players in them and you cluster plastic covers the face of the radio.
I just did an vintage auto sound (or is it custom autosound?) conversion. I haven't finished the wiring and speakers no sound feedback yet. It fits perfectly, no cutting. However, I felt the overall appearance was disappointing. The knobs are plastic chrome, and the centers should be black IMO like the original. No biggie there, the real issue is the horrible dash plate! It is a cheap flat ABS plastic rectangle with "chrome" sticky plastic, just janky looking stuff.
I'll probably piss someone off by admitting this, but I took my stock plate, and milled it out in the center to fit the new head unit. WAY better looking, and matches the patina of all the other dash parts. Not perfect, not nasty, just right, lol.