I'm very happy to see your going to keep the car stock, and that your really willing to do it right for the most part.
Painting it original is the best route to go, and believe it or not, that brownish/copper color is actually bad ass looking if it done right.
As for the audio, Fords systems back then were not the greatest, but if you don't mind your super high end system being in your other vehicle I'll give you some tips on what I did.
Ford did produce a factory premium sound system, with an amplifier "pull down" switch where your right knee would be under the bottom part of the dash, although crappy by today's standards, what I have done was to purchase an FM modulated 10disc changer by Sony and plugged it into the radio antenna for the system and replaced all the factory speakers with updataded units that fit the application perfectly (3 1/4" in the dash and 5"x7" in the rear quarter panels) still not the most stellar of sound systems but it does give you some cruising tunes to jam to, and still appears stock of all others gandering into the vehicle, I get compliments all the time about having a factory radio, and enough so to justify the $90 I paid on Evil Bay for the head unit, and another as a back-up, but it will actually be used in the 1979 restoration I have here, besides the fact you will have to actually cut the dash assy on that vehicle to make any DIN style work, which will ruin the dash assy unless you buy/find and old school shaft style radio, I still have a few here.
I noticed in the pics it actually looks like he has an after market radio in it already, and yes Ford put out quite a few systems back in the day so probably about 4-5 head units, including 8 Tracks, were optioned back then.
The TRX wheel and tire package is rare and expensive, rare that people are trying to find the wheels again cause everybody threw them away because of the metric tires, the 190-55-390's where stock on your car, the 220-55-390's came on the later 1983-1984 cars, and you can still get them through Tire Rack,
OR just pick up a set of 10 hole, 1985-1986 GT/LX wheels that every body is dumping, like what's on my little LX:
People on Craig's List or local Mustanger's practically give these wheels away, and since their 15" wheels, the 225-60-15's or wider are still under $100 per-tire.
Also another option, and the lightest factory optioned wheel is the turbine, 1987-1988 GT wheel, which was also later optioned on the rare limited production build, 7Up convertible Mustang of 1992 (I believe the date is right), I picked up a set of these wheels for free for our 1979 restoration, because they look just like the 14" steel wheels with the turbine hub caps, and I got a single wheel for $15 off Craig's List for a full size spare.
Now for the bad news, most all the parts are obsolete, the bumper covers, the out side belt molding, the tail lamp assy (1979 to 1982), the map light if so equiped, hood, cowl vent, any trim that is chrome, including mirrors, louver's are kinda hard to find (I just went through this problem), shift boots, the console delete shifter cover/e-brake cover, Cobra interior emblems, all the door panels, and interior quarter trim panels, the factory 2.5" twin tipped exhaust tail pipe, the seat material (I'll give you a link for someone to contact), since the best selling Fox Body was the 1987-1993, and the second best was the 1985-1986 most of all restoration parts are geared towards these vehicles, this means like myself you will have to search long and hard through salvage yards, peoples back yards, Craig's List, Evil Bay, and some forums like
www.foureyedpride.com for some of the parts.
Lemme tell you right now take the forums I linked up above with a grain of salt, they think they know everything, but they don't, some of their mom's were nothing more than my one night stands and were not alive back when these cars came out.
Not that I'm an expert, but I have spent many years with these cars.
Point in case, like a gentleman that works for a friend of mine in the Mustang restoration business asked me why I took my rear spoiler off my 85' LX, I told him I didn't, they didn't come with spoilers because the federally mandated CHML (third brake light) didn't happen till 1986, you could get a spoiler, but you had to beg with Ford to have that happen, he didn't know this.
Take a look at this little jewel, this is a late 1979 with, yes a 200cid straight 6, this was the 6 cylinder that replaced the roll-over V-6 found in the 1974-1978 Mustang II which is what we have in our 1979 restoration project, this car although deemed by "Hot Rodder's" as worthless, this car is actually worth a mint!!
I would pay good monies for this car:
It's hard to find them like this any more, there all molested or in salvage yards.
From 1978 when the 'New' Mustang was hitting the market:
Jeff - :navajo: