That's an interesting find! It has a chance of working. The important thing (as noted by HH56 below) is what is the stroke? Might not know until you get one.
Question: The specs list two piston diameters 0.625 and 0.875. I don't quite know what that means, but that could be some kind of inner proportioning valve. Also, the specs could be inaccurate.
In a standard dual master cylinder, the primary piston pushes on the fluid only, and the fluid itself is what pushes on the second piston, unless there is a failure in the primary circuit.
How Stuff Works - Dual Master Cylinder If it's anything like a standard-design dual master cylinder, the important spec is the diameter of the primary piston. If that's 0.625", then well worth a try. If it's 0.875", might not be. Also have to find a booster less than 7" diameter that would bolt up.
If you want to go ahead and try the 740 Volvo Cylinder, I would be willing to ship you my 7" Ford Courier Brake Booster, which I know fits in there on a 1953 and presumably also then a 1955/56, on the condition that if everything works well you would ship it back.
Those Ford Courier Brake Boosters are still somewhat available. What I saw for the Volvo 740 was 8" diameter, which wouldn't fit I am pretty sure.
1981/82 Ford Courier 7" Brake Booster #53-5211 (Autozone)This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=240863