Have you determined what it's pitched at? Given the age, it's very unlikely to be pitched at 440. It may be either "high pitch" ( A > 440) or "low pitch". But "low pitch" may be A < 440. If you can't tune it to A=440 then (depending how far out it is), it may not be useful for playing in contemporary ensembles.
I discovered that the easiest/most accurate way for me to determine the pitch on my 1926 Buescher Eb (the one I'm holding in my avatar) was to set the tuner to a particular pitch, and then to attempt to play a scale (or several scales) without "lipping" the notes. See how close the notes come to the center of the pitch for that note. If you can't pretty easily play a good scale, the change the pitch (setting of the tuner), and try again. When I got to A=435, my 1926 horn produced an accurate scale. The horn then met Mr. Hacksaw. That horn is labeled "LP" (Low Pitch) on the 2nd piston. I was hoping for A=440, but ... .
If what you really want is to restore a rare and interesting old instrument, then probably interaction with Mr. Hacksaw is not the direction you want to go (besides -- that won't work for a high pitch instrument). But you should discover what pitch the horn is built to, and then let that guide you in trying to use it in various circumstances.
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)