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I'll try to answer some questions. The Moldau large leadpipe is nickel-silver. The smaller M (medium) leadpipe is rose brass. They have a tested formula which determines which leadpipe/bell configuration
/bell or body alloy works the best, balancing each other. Unless special ordered otherwise, the standard Moldau has a slightly smaller-diameter Yellow brass bell, plain rim, and the L (nickel silver) leadpipe, or the M leadpipe and yellow brass bell with nickel-silver rim.. The Moldau 784 has a rose brass body & bell, and the L leadpipe. The 884 Moldau Deluxe has the rose brass bell, plain rim, L leadpipe and yellow brass body.

Please feel free to contact me with further questions.

So if the 684 that Mark liked better had a silver leadpipe but no silver kranz, then both the 684 and 784 he tried had the same L leadpipe.