Intro and Valve Adjustment Help

[rotor_kin]

Hello all,

I've been poking around the forum for a couple of months now, learning a ton about my new (to me) 71 c20 pickup with a 402 and TH400. As a quick backstory (jump to the last paragraph if you wanna skip the story and get to the goods)

Bought the truck in Christmas eve for a great price. Drove the truck same day back to fort worth and changed the oil, checked fluids, and got some new tires. The next week I drove it the 200 miles down to Austin and the truck ran like a top and didn't skip a beat, I was so proud of it! Since then I've been fixing small things here and there like carrier bearing, heater fan, etc...

As of late I have been digging into one issue thats been lingering which is a pretty rough idle. The idle mix screws seem to make little difference, and turning the idle speed below about 900rpm ends up stalling out every once in a while at a traffic light. The truck runs well outside of this, however I am also not quite sure the secondaries are opening on the quadrajet.

Long story short, now is a perfect time for me to learn more about this truck and get it going strong as I have another car I can use if any fixes cause major downtime. I called cliff of cliffshighperformance to get a rebuild kit and some advice, and he told me the carb on my truck after giving him the carb stamp, was from a 78 chevy and seemed like a californian emissions carb (the carb number really had him stumped, said he hadn't heard that number before?). So I am working with him on getting the carb setup to run well with the 402. While I am at it i figured I would double check the valve lash as I am not sure what the PO had done mechanically. This is where I run into my current conundrum:

Looking at the lifters it appears as though they are hydraulic. They have the small wire type clip, and none of the valves had any gap between the roller and the valve stem. However none of the valves also were very tight, all of the push rods would rotate pretty freely. So it seems like the valves were adjusted to be snug and left there. The one thing that seems weird is when I go to adjust the #1 intake valve (as if it were hydraulic) I see no movement in the pushrod after snugging the rocker bolt, and clearly see the valve spring compress after about a 1/2 turn past snug. I wanted to get the advice of the forum before I went adjusting the valve lash one way or the other to make sure I'm not crazy. I've attached a pic of the lifter looking through a fancy bore scope my buddies got me for xmas.

Any advice would help. I am new to american cars, but have worked on a few older japanese and european cars, and a boat load of 60's and 70's motorcycles so I have a decent mechanical compass. I know that once hydraulic lifters are set they rarely need adjustment, but mostly I am interested in learning how to do it and learning more about my new toy. Thanks