This reminds me of the guy who married a Ford Capri (South African Peranha spec, with the same 5 litre V8 as found in Mustangs) floorpan, bulkheads and other structural pressings with the carefully removed bodyshell of a split screen '54 Morris Minor, itself also a unitary so that job wasn't a relatively simple chassis and shell swap. That car has now been running for a good twenty years in its hacked about form, I suspect that this mad crossbreed boombox will be every bit as wild if a little safer on wet roads, Lovin' it!
Not just loving it but inspired by it as I have the working contents of a collision-damaged PC-11 that I recently bought from eBay purely for its rear wiring cover. I also have one of those early '90s Hitachi boxes with the "Turbo bass" labels and four speakers across its front, all kicking out the exact same muddled noise.
Anyway, its cabinet is deep from front to back. Deep enough for some decent electronics. If only I didn't have several thousand jobs that are more important and need to be done before I drown under ancient electronic landfill candidates.
Good luck with this one, I too shall be watching with interest for more on this crazy, yet brilliant build!