I also have 6x9s in my 68 and I don't remember what kind either. 

I've run many different brands over the years.  Currently I have two JBL 6x9s in the back and a JBL component set in the front with a single JBL 10" sub in the trunk.  I can't say I ever had a name brand set of 6x9s that I was unhappy with.  Pioneer and Kenwood are on the lower end of name brand.  JBL and Polk are on the middle/upper end.  With speakers the more expensive brands are going to be made from better materials and will sound better and last longer, but sometimes you are also paying a premium for the name.

6x9s are typically rear speakers and in audio terms qualify as "rear fill".  Rear speakers are mostly just to balance the sound so its in an enveloping experience instead of directional.  A properly designed system will seem like you are surrounded by sound to where you can't tell where its coming from.  Front speakers are MUCH more important than the rears.  I prefer components in the front because I can mount the tweeters to basically hit your ear so you can't direction find where the sound is coming from (the higher the sound in Hertz the more you can tell where its coming from), and then mount the mids in the doors or kick panels.  Low sounds you can't tell where they come from, which is why a sub in the trunk isn't much different than one under your seat. 
 

Bentworker wrote:

What kind of wattage are you going to throw at them? That is a big part of the decision making process. The speaker you would use with 20 watts a channel is different than 120 watts.

For me I have used Alpine type R speakers in my last couple daily drivers. They are odd because they use neodymium magnets, which are small for their strength. It just means you end up with a smaller (depth wise) lighter speaker that performs well. I’ve been happy with them, and in my van I have about 600 watts spread around to 4 coaxial 6” speakers, two component 6” speakers and two 1” tweeters. Speaker placement is a HUGE part of controlling sound. You can buy the best stuff in the world and if you put it in the wrong places it will sound like garbage. There is a guy on YouTube with a channel called CAF or Car Audio Fabrication. He does a good job of explaining the what and why of car audio.
https://youtu.be/rZcga_2NbqU
 

This is the stereo I am getting.


https://www.cjponyparts.com/custom-autosound-radio-usa-740-am-fm-1965-1966/p/USA740A/

 

Wow, they are super proud of that.  A typical single DIN head unit from Alpine, etc. is like $120-$200.Example here:

https://www.crutchfield.com/p_500UTE73BT/Alpine-UTE-73BT.html?tp=72430

You can't just look at peak power output.  Peak power is its max output, and is intended for a very short period of time.  Drive it at peak all the time and it will fail.  If peak is 45 or 50 watts RMS is probably less than 20.  Again, my advice would be get a 4 channel amp capable of 100-150 watts per channel peak.  Its more money, but you will spare the head unit the heat and make it live while having adequate volume.  Case in point, the volume in my car is 0-40, but I've never turned it up past 25, and normal cruising its at maybe 15-18. 
 

20-25 years ago I'd agree that I'd rather listen to the engine, but if around your way is anything like mine is now traffic is unfortunately a part of life.  So if I've got to sit for a spell I can at least listen to decent sounding music. 

I fitted the under dash speaker and two 5-1/4" speakers (260W) in the rear parcel tray, along with an amp.
It is a very clear sound coming from my stereo. Love it...

TKOPerformance wrote:

Wow, they are super proud of that.  A typical single DIN head unit from Alpine, etc. is like $120-$200.Example here:

https://www.crutchfield.com/p_500UTE73BT/Alpine-UTE-73BT.html?tp=72430

You can't just look at peak power output.  Peak power is its max output, and is intended for a very short period of time.  Drive it at peak all the time and it will fail.  If peak is 45 or 50 watts RMS is probably less than 20.  Again, my advice would be get a 4 channel amp capable of 100-150 watts per channel peak.  Its more money, but you will spare the head unit the heat and make it live while having adequate volume.  Case in point, the volume in my car is 0-40, but I've never turned it up past 25, and normal cruising its at maybe 15-18. 
 

    Thanks for the link!  I think Im buying that Alpine for mine!