Dumping the lifters in soapy water wouldnt be on my "to do list". If you're dead set on cleaning them out, you can actually disassemble them by removing the retaining clip, and then wash the individual parts in solvent. Dry them off and fill the lifter with oil and reassemble. Then when you're done with re-assembly, submerge them in engine oil, and using a pushrod while holding the lifter vertical (yet still submerged), push the plunger up and down to expel as much air as you can and to get them filled with oil. Holding the lifter vertical, given its a roller, (and you dont want to scratch them all up with pliers), wont be all that easy.
But this is still a bad idea. I would just wash them off with solvent and check all the plungers. then drop them all in a tub of oil, and do the plunger depressing job to hopefully replace some of the old oil with new oil. if it were me, i would just wash them as use them as is. If they get noisy down the road, after the break in oil has been flushed, throw a quart of marvel mystery oil in the engine with the next few oil changes. That stuff works wonders for sticky dirty lifters.
Of course Im assuming you have used lifters. otherwise, i dont know why you would want to do any of this. If they're new, just spray them good with WD-40 and blow them off with an air gun. then lube them and install.
If the shop hasnt done this, using a fine file, deburr the sharp edges of the bearing saddles on the block, and the main caps. Right where the 2 bearings join, on both sides. Make a tiny chamfer maybe .010" wide. Best to lay the file at a 45 degree angle, with the file laying in the direction of the engine, front to back. Run the file from the front of the motor to the back, so that the file is being supported by another main web as you run it across. helps to get the chamfer the same size on every main web, and keeps you from making any burrs when you run the file in that direction. Do the same (very carefully and be extremely clean!) to the bearings themselves. Just a tiny little chamfer on the sharp edge of the bearings, where the 2 bearings meet, on the inside. Dont make a .010" chamfer here. Smaller. Best to have a fine and clean diamond file when doing this. When the block is torquing and twisting, and when over time the block (line bore) starts to warp, this can help prevent the sharp edge of the bearing from scraping the journal, and scraping the layer of oil off the surface. If you're not using the rope seal, I would recommend staggering the 2 main seals. You install the seal, and then rotate it so maybe 1/4" of the seal is above the surface. Do the same to the one in the block. Now when the cap goes on, the seam where the seals join are not inline with the seam where the main cap meets the block. This will stop any future rear main leaks. These are a couple tricks we would do on every engine.
If you have never assembled an engine, dont even THINK about doing this yourself without a seasoned engine builder by your side. There are so many things that you will never read about that can make all the difference in the success of the build and longevity of the motor.