Correct- .0018 on the mains and the rods. Machine shops are used to doing the machine work on SBCs, as there are a million of them out there. The SBC isn't as stressed as the 3.8, and can therefore live on much looser tolerances without any adverse effects.
From Jack Merkel: Merkel likes to see no more than 2 thousandths clearance (1.5 is preferred) in the main bearings due to the fact that there are no 3/4 groove main bearings available for Buick V6s. (We should note here that 3/4 groove bearings should be available from Federal Mogul by the time you read this.) Oiling for the rods is very important in a Buick because six rods are doing the work of eight. Merkel says, "These engines don't see a lot of rpm so the important thing is to keep the main clearance tight to ensure adequate oil volume to the rod bearings. Typically a small-block Chevy will run a higher rpm to produce the same horsepower on the motor, so they need more clearance."
GM Hi-tech Performance mag article
HTH
