I've bought 2 dart blocks.They didn't need any machining on the decks,(i did have them decked to get the proper finish), or the mains.I talked to my machinist about the dart and merlin.He said the merlin was cheaper but he said on the average needed more machine work,also said the dart has better oiling system(not sure what that means),has a higher nickel content and is just a nicer casting. I'd call the machinist you use and ask him.If he isn't familiar with aftermarket blocks i'd find one that is.
Then go with the dart. :grin: