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I trust that your original 321 leadpipe's in good condition.

It so, just order a Weril H980 receiver--forget the leadpipe. The Weril receiver is sized for a leadpipe end just a tad smaller than the Yamaha, so you may need to slightly enlarge the Weril part. This lets you keep the original leadpipe on the Yamaha (and avoid messing up the finish by replacing it). If done carefully, the alteration won't be visible to the naked (or fully dressed, for that matter) eye.

KJ wrote:Would there be no benefit to installing a larger leadpipe? I find the horn to be less than free blowing at times and am looking for a reasonable solution without having to upgrade to a new horn...can't really afford to do that right now.

How (and why) would a larger bore leadpipe do anything? How would you match an overlarge leadpipe to the valve set, all of whose branches are the same old small bore? I can imagine that a leadpipe with a different taper might have a definitie effect, but a leadpipe still has to start at the receiver and match up at the first valve...

The leadpipe on the Yamaha 321 euphonium is actually quite large, just replace the receiver and you will be able to use standard mouthpieces on it. With a little adjustment, almost any receiver that your repairman has lying around should fit on there.

I may just be stating the obvious, but I'd suggest making sure that the present equipment is clean (a little internal slime film can affect the blowing resistance), and make sure that the valves are properly aligned. A properly-functioning YEP-321 should be quite free-blowing, indeed.