There are many good brands out there, but I like Alpine for the money. They have a good range of prices and features, and quality of sound is very good, but that depends more on speaker quality.

What I did with my '78 was buy a new center console bezel and carefully cut the proper size opening. It looks great. Now you can buy pre-made console bezels for these new stereos. That what I did for my '69 and installed an Alpine in that also. My '69 is a big block as well and the stereo needs to cranked up to hear it, especially with the top down.

I think this is what you're going to have to do if you want quality sound. I don't think you'll find it with factory type radios.

74-454,

I agree with Gunslinger, you won't get a quality sound with any factory type radio. Before replacing mine I researched for about 6 months, and Autosound didn't cut the mustard. I have the same C-3 has you, 74-454 with headers. You can fit a set of 4X6 speakers in the kick panels without cutting or modifying anything. Infiniti's are the shallowest, I bought a replacement bezel and cut it out for the Alpine that I had. I posted a picture of how I installed my rear 6X9's Infiniti's and Amp. without having to cut or modifying the rear. The result is a superb sounding system, and it looks good.