Right now I believe DART is only offering the Clev main, although the older castings were both. You'll like the Clev mains, it will help keep the bearing speed down and solve some on the issues associated with a 3" main. Since it's a DART as long as you set it up for prioirty oiling the mains will be fed nicely, .002" is just a little low for what I like to set them up, even on a street car...will it be fine? Yes. The reason I mention the clearance is I have NEVER had a DART block in my shop that was not tight on the mains, they are always on the low end of O.D, and I have to align hone them. I check everything with a dial bore however and mic's, not plasti gauge. Just have your local machine shop check it to verify your clearances... You'll find you'll need to deck the block as well, the surface finish is just no where close to having a good sealing surface, plus if it was me you'll want it "0" deck.
Here's a couple things to look out for on the DART... The threaded plug that will go into the front of the oil galley right behind where the dist gear sits, make sure you use a shallow 1/4" plug, they are actually NPS threads and if the plugs sits out it will not clear the dist gear. With a 4.00" stroke and a 6.00 or 6.25" rod you may not even have to clearance the bores for the rod bolts, although it is always best to check. Just don't be surprised if you don't have to.
Although this is standard block prep make sure you deburr the edges of core plug holes aka "Freeze plugs" really well, along with the rear cam plug and the ouside surface edge of the rear cap where the 1 pc seal will go if using a 1 piece seal crank. They are sharp and always a little tight, if you do not chamfer or deburr it will shave the edge of the seal and plugs upon final assembly. Check the rear cap for rough metal above ther journal in the oval holes, there is usually slag there as well. The rear cam plug if your installing is a reverse taper plug, so the hollow side goes in first (this is the reverse of a standard Windsor motor), they can be fun, if your installing it I suggest getting 2 just in case.
If it is the IE block, radius the edges (the edges facing the rear of the block) of the 5th main cap to prevent pan clearance issues, and on most 1 pc gaskets you'll have to notch the gasket to fit around the 4 bolt cap.
If you run into anything specfic and need help let me know...