I would work with the low end of the standard
oil-clearance spec with an aluminum block. But don't forget
oil viscosity and application. More engines have been killed with high-viscosity
oil and tight clearances and vice versa. Starting a cold engine with tight clearances and cold oil will cause scuffing. Cold oil will have a hard time squeezing into those tight clearances. And there's nothing like experience. Go with what works.
When checking clearances, do it with the block at about 72 degrees with the bearings in place and the main caps torqued to spec. Otherwise there's nothing to it.
For a good idea of clearances check out Childs & Alberts web site:
http://www.childs-albert.com/catalog...gs.pdf#search='aluminum%20block%20oil%20clearance'