You really can't tell if just cutting the main slide will work until you try it and the various scales and pitches. My guess is that it probably won't. I ended up cutting every slide on my 1924 low pitch Buescher tuba. The real trick will be on the 2nd valve because the slide is so short.
And you may not be happy with the result under of the best of circumstances. Sometimes it works well, and some times it doesn't -- and you'll have intransigent intonation problems, especially with valve combinations. That horn was built to play at a specific pitch and may resist playing completely successfully at another.
There's a lot of trial and error in this, and NOBODY is likely to get it right with just one cut of each valve slide.
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)