how / where do you set the fuel mixture (richer / leaner) on a 1968 4 BBL rochester quadrajet carb ?

Doesn't sound like you're up to changing jets or metering rods so I'll answer with... a carb shop.

there should be a couple of small spring retained screws on the front of the carb I forget which is which but you'll need one of those carb adjustment tools from autozone

The screws are only found on 1968-70 models. 71 & up GM capped the screws (I hink you can breeak off the caps) supposdly as an "emissions" bullcrap thing.:annoyed:

Yes, that's true. They ARE in the same place but capped off. The caps are removable and then you'll need a special tool to adjust the screws since they have either a "double-D" or "hex" head on the screws. Beyond that everything else is the same as on older carbs.

Keep in mind these screws adjust the idle circut only. Why do you feel your mixture needs to be changed? I'm more inclined to suspect carb malfunction in most instances......