There is some degree of debate concerning the pros and cons of replacing a smaller receiver with a larger one. In general (as you can see) the recommendation of people with some experience is that you don't do this. And to some degree this depends on the particular model of the instrument. For some, it's fine to do the replacement. For others not. Unless you've got a good reason compelling the change, it's probably best not to do it.
My own approach to this you can see below. I have a Mack Brass compensating euph that takes a large shank mouthpiece, and an Amati oval euph that takes a medium shank. My Doug Elliott mouthpiece works on both since I just switch shanks. Not the least expensive solution, but it gives me absolute uniformity in terms of the feel of the mouthpiece.
I've thought of doing the similar switch on my old 1924 tuba which has the original "small British" receiver since it would give me a MUCH broader selection of mouthpieces to choose from. Ultimately I decided against this since I found a mouthpiece that works well with it and I just didn't want to do any more "invasive surgery" on that nice old horn.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)