For the rear clutch (forward gears), I like it very tight. 0.025-0.035". Most of my builds are in the 20's. Too much travel works the belville spring, and way too much can cause it to go overcenter. Changing a standard 0.068" steel for an 0.088" will put you where I like to be. And they do make .070somethings.

The particular year factory manual I have says 0.025"-0.045" for 4 disc in the rear clutch.