Is it a TBI vin Z or a CPI vin W? Sounds like you might have the older style valve train. 1994 was a transition year.
20 ft.lbs. is correct for the vin W and some (not all) 1994 vin Z engines. If your studs aren't bottoming out easily and you are having a hard time adjusting them you may have one of the TBI engines that still uses the old SBC method of adjustment. Not the newer fixed valve train method.
If that is your case and you tighten the studs down, all HECK will break loose when you attempt to start it.
If this is the case, use the following procedure to tighten the rocker arm nuts and properly center the pushrod on the hydraulic lifter:
Disconnect the negative battery cable for safety.
To prepare the engine for valve adjustment, rotate the crankshaft until the mark on the damper pulley aligns with the 0° mark on the timing plate and the No. 1 cylinder is on the compression stroke. You will know when the No. 1 piston is on it's compression stroke because both the intake and exhaust valves will remain closed as the crankshaft damper mark approaches the timing scale.
With the engine on this compression stroke, adjust the exhaust valves of cylinders No. 1, 5 and 6 and the intake valves of cylinders No. 1, 2 and 3 by performing the following procedures:
Back out the adjusting nut until lash can be felt at the pushrod.
While rotating the pushrod, turn the adjusting nut inward until all of the lash is removed.
When the play has disappeared, turn the adjusting nut inward 1 additional turn for 1988-93 engines or 1-3/4 additional turns for 1994 engines.
Rotate the crankshaft 1 complete revolution and align the mark on the damper pulley with the 0° mark on the timing plate; the engine is now positioned on the No. 4 firing position. This time the No. 4 cylinder valves remain closed as the timing mark approaches the scale. Adjust the exhaust valves of cylinders No. 2, 3 and 4 and the intake valves of cylinders No. 4, 5 and 6.