Well I know I can fit in the speakers easily but what about the head unit? Is there a place where I can buy a modified frame for the head unit or will it just have to be a DIY. Thanks.

You might wanna make a wooden or metal plate that fits in the original console. You can either cover it in vynil so it looks original or use a nice wood like mahogany that looks nice. Pretty easy to figure out what to do from here.

What are the dimensions for a slot for a head unit?

Hmm...i dont know the exact dimensions, but if you already have a head unit, just take the sleeve its supposed to slide into and trace it onto whatever you are using.

www.crutchfield.com Type "underdash" into the search box. That's what I used.

My headunit installed
http://img481.imageshack.us/img481/7379/dsc039042dx.jpg (http://imageshack.us)
I had to spread the console a bit to get it in. I put screws through the side of the console to mount it. The holes were already there, so no harm done. You can probably make a bracket that will hold it in place from inside the console.