If an audio equipment manufacturer does not publish detailed specs for its products, that is usually because sound quality is not a priority. I went with a RetroSound Model Two (received yesterday) since it appears to be a much higher quality unit with honest specs. The Vintage Vibes units tout 200 or 300 watts, and you can bet that is peak power rather than RMS (continuous power). RMS ratings are considered to be true power. Peak power (the maximum power a piece of equipment can deliver for an instant) is used to make an audio product seem more powerful than it actually is because most folks believe that larger numbers are better. Since even the Vintage Vibes website does not reveal RMS specs for their head units, I would not even consider one.
Very few head units have enough power to allow music to be heard cleanly over road noise (especially in an old Jeep with the top down). I've always installed separate amps under a seat in my Jeeps. This time, I chose the Rockford Fosgate PBR300x2 that will produce 100 watts RMS into 2 channels with a 4 ohm load. It also arrived yesterday. There was a Rockford Fosgate amp in the Jeep when I sold it, but it was removed and given away by the guy who lovingly cared for my precious Scrambler for the last 20 years. He wasn't an audiophile.
Many years ago, I built custom speaker boxes for the Scrambler that house 6x9 speakers. They are 29 inches long and fill the area between the door sill and floorboard, from the front of the door to the seat belt anchors. They are still in perfect shape but I intend to pull them next week, sand them down, and re-varnish them. They will then get a set of new Polk DXi691 speakers. I will post some pix of them during the re-finishing process, and after the re-installation.
After listening to the new system, I will decide if I want to install a separate powered subwoofer. I don't think I will need to do so since the Polks have a frequency response down to 35 Hz and the amp will produce plenty of clean power.
If you push a Vintage Vibes unit even close to the point of producing the advertised 200-300 watts, the music will be HIGHLY distorted...and you stand a very good chance of damaging your speakers. Personally, if I'm cruising down a canyon with the music cranked and singin' "Don't Fence Me In" along with Willie and Leon, I want the coyotes, rabbits, lizards, and the occasional Big Horn to be able to understand the lyrics.