www.chiltondiy.com and purchase for $19.95 the entire manual, with access for one year.
It is 4.5".
5x5
Not without modification
should be mounted in the fuse box.
go to manheimgold and figure out the price.
go to the library and get a chiltons repair manual for your year car.
find an appraiser and get it appraised.
Try Yearone.com
Get a chiltons repair manual for 1970 chevelle at the library.
Classicarwiring.com (eBay)
It's in the Bentley manual for Type 1 1970-1979.