Here is the reasoning behind the revised lash spec.
The lash specs are designed to match the cam and the rocker arm ratio. The solid lifter cam lobe has a gentile clearance ramp area at the base of the lobe and a much faster lifting ramp for the portion where the valve is off its seat. Basicaly the clearance ramp is where the valve train takes up the slack as the valve lash is closing up when the lifter starts moving. The clearance ramp on the "30-30" cam is exactly .020" high on the base of the lobe. The lifter will be lifted .020" slowly until the lash is taken up and from that point on it is moving much faster up and then down until it gets down near the seat. Just before it gets down to the seat, the ramp speed will slow down in order to set the valve down on the seat gently rather than at full lift ramp velocity. This is done to avoid valve bounce, recession, and noise.
We typicaly measure the valve lash specification in the area between the rocker arm tip and the valve stem with the lifter resting on the cam's base circle. The clearance at that point is the lash spec. Since we are measuring it at the rocker arm, the clearance at the cam is mutltiplied by the rocker arm ratio. The design specs of the factory rocker arm are 1.5:1 ratio so a clearance of .020" at the lifter side of the valve train is .030" at the valve side (.020" x 1.5 ratio = .030") so far, so good! So what we are saying is we want to have the valve lash set so that all the clearance is taken up at the exact point on the cam lobe where the transition from slow to quick ramp speed occurs. It can be a few thousanths tighter and still be on the slow portion of the clearance ramp but if it is too "loose", the clearance will not be taken up while the lifter is still on the clearance ramp and the cam will be noisy, the valves will receed, the valves will also likely bounce on the seats at very high RPM as they are being slammed down at lift ramp velocity.
The problem comes from the actual measured rocker arm ratio of the factory style stamped steel rockers. The design spec is 1.5:1 ratio but the actual measurement is closer to 1.37 instead of 1.5 so the lash spec must be changed if you use stock style rockers. Now, if you are using the stock rockers, the best spec is determined by mutiplying the lift ramp height (.020") by the "actual" rocker arm ratio (1.37) and you get .020" x 1.37 = .0274" which is the MAX lash spec you would want. Set the valve lash at .026"/.026" COLD.
WARNING! You CANNOT, repeat, CANNOT accurately adjust EITHER the inlet or exhaust valves of the 30-30 at TDC because BOTH the inlet and exhaust are on the ramps. If you adjust at TDC your actual running clearance will be about .032" to .033", but the MOST you want is .027". Adjust the inlets at 90 degrees ATC and the exhaust at 90 degrees BTC. Lay this out on paper and you will see that you can adjust two valves at every TDC point as follows:
TDC#1 8E, 2I
90 4E, 1I
180 3E, 8I
270 6E, 4I
0 5E, 3I
90 7E, 6I
180 2E, 5I
270 1E 7I
Start at TDC #1 and adjust 8I and 2E, then rotate 90 degree and continue with the valves as indicated. Set them at .026"/026" cold with the engine not running. You can also use this method for the LT-1 cam, but you can adjust the inlet at TDC if you like because of the LT-1 cam's shorter inlet duration and clearance ramps. Recommend .021"/.027" cold clearance with the LT-1 cam to adjust for the actual 1.37 ratio at the end/beginning of the clearance ramp. Mark your balancer at the ninety degree points with tape. Do it as accurately as you can, but if you're within ten degrees, it's okay.
To visualize the reasoning helps. The adjustment follows the firing order 1-8-4-3-6-5-7-2. The idea here is for you to get the engine on a firing position TDC for a cylinder, lets say #4 for example, and then figure out that the cylinder that was previous in the firing order(#8) will no way be on it's intake ramp and the cylinder that is next in the firing order(#3) is no way going to have it's exhaust valve on ramp. This is how I can easily remember which rocker to adjust without writing it down. Once you get the concept(takes a while) you might not need the sheet of paper anymore.
Feel free to ask questions if you need clarification.