58 GMC 1/2 ton truck, 3speed with manual OD, gmc302 30over, 3/4cam, 9:1compression, Clifford Intake/Headers, HEI ignition,
Need recommendation on a 4barrel carb. Langdon stated Holley390 or Edelbrock 600.
Thoughts?

Q-Jet off of a 3.8 buick V6. Or a 305 sbc. It'll run rings around a holley.

I have a very similar build on a '57 270 in a '53 Chevy pickup. I'm running a 500 cfm Edelbrock. There are lots of jets, rods, and springs to dial it in.

A Q-Jet for a 78-79 305 with an electric choke would be ideal. In 78 they were used in Olds Cutlass in 79 used on Chevy Malibu cars. The air valve is set to about 500-550 cfm a little more than needed but will work good. With the adjustable part throttle any flat spots could be cured and get good gas mileage when cruising.
I also agree with beater that the 500 Carter AFB from Elderbrock would also be a good choice. (I don't care for the AVS) very easy to tune with excellent support and tuning help from Elderbrock. If you are uncomfortable with the Q-Jet go with the Elderbrock. I have had good luck with both. I am currently running a Dualjet which is the front half of a Q-Jet but that would be too small for a 302 unless you tried to run 2 of them. Jay

X3 with the 500 cfm eddy.

Are you set on the 1x4? The reason I ask is that you might consider a 2x1 intake, some adapters and a pair of 1974 pinto 5200 Holley/weber carbs. Those are progressive and a pair on your motor would work pretty much out of the box. I started with a vintage weiand intake for my 261 with that set up and it ran very well with nothing more then an idle adjustment. Those pinto carbs are progressive with a primary and a secondary, running two of them is not troublesome and the look is terrific. I am not sure how to post pictures here but if you send me a message with an email I will send you a photo of the set up I was using.

That being said, and I do not know the answer to this, you might call clifford and see if they sell a 2x2 intake for the GMC. I purchased one last year for my 261 with a pair of 38mm weber DGEV carbs (non-progressive). Runs unbelievably well. Has a water chamber already cast into the bottom of the intake and you can run a few types of two bbl carbs, you just switch adapter plates. Same deal with the photo, I can show you that intake as it is on the motor now.

2x2 would sure up the cool factor! 2 of those square air cleaners would sure look good! Please let us know what you decide to do. You may not want to spend the money for another manifold. Jay

The dual 5200 looks really cool. The 1974 versions have a threaded inlet which makes plumbing them a lot easier then the earlier versions that had the pressed in brass nipple. And, they run great out of the box, at least for me and my motor is pretty modified.

I was also not enthralled about having to shell out a good bit of money on the new Clifford set up. I sold a bunch of other intakes and parts and got the Clifford set up. All I can say is that for me it was money well spent. The dual weber DGAS 38 mm carbs are just tremendous runners.