MLS and O rings are used quite frequently in the import world, most domestic guys think you are crazy doing so, but results don't lie. I would have you block decked, and still do the surface prep like you did with the wd40. Going to a larger stud (1/2") is a great idea, especially with the larger 87mm bore you are using, but if a goal of 5-600whp is all you want, I wouldn't waste my time. I would go with a simple MLS gasket and mirror finish on block and head. As far as re using your old rods, I would absolutely do so. They have unlimited life for the most part, and can almost always be fixed. I would be willing to bet you don't even need to get them honed or resized, simply swap out bearings. As far as pistons go, check for skirt wear and make sure your PTW is still in spec, mainly deviation between cylinders. I'm willing to bet they are just fine. Because of the crappy tuning youve had in the past, I would be inclined to hone your block and get new rings, depending on how the bores look. Lastly, because your block and head will be decked/milled, I would look into adjustable cam gears so you can degree your cams in. Pick a head gasket that maintains proper quench of around .035-.050, but don't buy that until your block is back from being decked so you can measure from the top of the piston at TDC.
that should be all?
Looking great though!