I recently upgraded/replaced the head unit in my van (1992 E150 w/5.8) but everyone i talked with told me that i would have to trim the opening and make it bigger, i did have to pull the dash trim plate but didn't have to trim a thing and it actually fits beautiful just like the factory head unit, the stereo is a kenwood kdc-x597 with removeable faceplate and it is easily removed and reinstalled.
Also added an 1100 watt 5-channel amp and a pair of 12" subwoofers in a sealed enclosure, it's a 2-way active system with no coaxial speakers and no passive crossovers, it is strictly 1 speaker per channel and the active analog crossover built-in to the amplifier handles the low pass high pass and band pass dividing chores.
The first 2 channels are 4 ohm Vifa tweeters resting in both corners of the dashboard inside a wedge shaped fixture 4" tall and 6" wide that i made from the flaps off a cardboard box and the door speakers are CDT Audio CL-5 midrange drivers occupying channels 3 & 4, the 12" subs are a pair of 4 ohm but wired in parallel for a 2 ohm load on channel 5..
To say that it is extremely loud and clear as a bell would be an understatement, it is audiophile grade music reproduction with rock concert SPL's, imagine standing directly in front of the huge speakers with the sound so loud you can't hear yourself think, that's kinda what it's like sitting in the drivers seat when i crank it up. I have not done any electrical mods other than running 4 gauge cables from the battery to a location on the sidewall just behind the drivers seat.
With 75 watts x 4 channels for the tweeters and midrange drivers plus another 500 watts for the subs equals a 800 watt maximum power divided by 14.2 running voltage equals a 56 amp maximum current draw but that would be at 100% volume so let's crank it back to a reasonable 75% volume level which drops the max current draw to 42 amps, that would be with the volume at the 3/4 mark, so using a 75 amp alternator (as an example) that still leaves a minimum of 33 amps available for the rest of the vehicle.
Here's a breakdown of the entire system:

Electrical Mods: None as of yet
System Config: 2-way Active
Head Unit: Kenwood eXcelon KDC-X597
Interconnects: Stinger 6-channel
Amplifier: MB Quart Onyx OA1100.5
Tweets: Vifa BC25SC06-4
Mids: CDT Audio CL-5
Subs: MTX TNE212D modified Compound Push/Pull

I do have plans to install another battery with isolator very close to the amplifier along with a stiffening cap, i was one of those skeptical people that thought stiffening caps were a joke and the early ones were but times change and technology improves and now people are replacing car batteries with capacitor banks, i didn't believe they did a thing until today when i watched a video that used an amplifier dyno to actually measure rms wattage output with and without the stiffening cap, my jaw dropped a little bit because adding the cap actually make a substantial improvement and increased output power, some people are using a maxwell ultracapacitor which is a new technology combining a battery and capacitor in the same housing, there are pros and cons to the design but it does appear to make it's own mark on renewable energy systems of the future.

 

MTX TNE212D with 1 sub turned around and wired out of phase so it's mechanically in phase, it's a compound push/pull design that i am evaluating. low pass from 20Hz to 150Hz





CDT Audio CL-5 midrange drivers, they play bandpass frequency from 150Hz to 3kHz





no modifications are required to install aftermarket head unit, just remove the dash trim plate, upgrade head unit and reinstall trim plate





Vifa BC25SC06-4 silk-dome horn-loaded tweeters, high pass frequency from 3kHz to 20kHz,





MB Quart OA1100.5, sorry about the focus didn't notice until after i uploaded





gives you an idea of the size of the wedge i built for the tweeters, eventually i will mount the tweeters in dash in each of the 2 a/c vents, 1 on each side





drivers door CDT Audio CL-5 midrange driver