Hint with Nissan Motorsport cams the checking clearance seems to be 20 thou, I arrived at that by changing clearances till I got the correct duration and then set the cam taking special care to make sure the Inlet valve closing point was correct as that has the most effect.

Closing point affects effective compression ratio and hence torque and overall performance it is by far the most important timing point in any engine, Some people use a simple but foolish method of setting cams with equal lift on number four cylinder do not do it that way as it will result in less power and a drop in torque, I did an L series that had been set up that way with a works 76 degree cam and after dialing it in to correct factory timing specs it came on the cam almost 700 RPM earlier than it did set up incorrectly, So it really is worth the effort to do correctly.