Hello George,
Well, the truth of the story of the tumbler barrels is: they are not designed to (be disassembled).
Rather these were designed to be replaced by a new unit (e.g. new door handle with tumber barrel).
When new the five little brass lock pins (for the old style sytem until 1967) were pressed in together with their little coil springs into the tumbler barrel and fastened/punched/sealed with a kind of hammer stroke.
You can see this stoke on the top surface of the diecast tumbler barrel after cleaning the barrel with some detergent/gasoline etc.
In old tumber barrel assemblies these often break open themselves and the lock pins and springs can/will fall out ... depending on the remaining amount of grease or dirt....
Theoretically you can break this kind of "seal" and replace/rearrange the lock pins but it is a bit tricky.
But this doesn't help you at all if you don't have the correct lock pins for your new (or desired) key. You "could" theoretically fabricate yourself one out of a couple of donor parts but still those won't be like new as these tumbler assemblies wear out (heavily) with the years/decades/half centuries...
Perhaps a good (and specialized) locksmith can help further.
Good luck and keep us updated
Achim
(has not had much luck with his used lock assemblies)