I suggest you take a breath and go back to the fundamentals. This roof has apparently been there for 50 years, so clearly it is strong enough to survive. Before you go "repairing" it, consider the simple question, if it is so grossly underbuilt, why is it still there? There is a lot of strength in old growth wood that is not reflected in current codes, which generally assume you will be using relatively low quality, currently available lumber, so this roof may be built with stronger lumber.
Second, the only significant vertical load on a roof comes from snow and ice, and the occasional impact from a falling tree. I exclude tornadoes and other serious wind events, those loads are complex, and are generally not considered vertical loads. So here is a possible option. The next time you get some snow on the roof, hire a local unemployed person to shovel off your roof. You can do this with a snow rake without even getting on the roof. That should extend the life of your roof through many more winters, at least until the roofing fails, then you get that replaced.
Since you lack the funds to properly frame the project, but clearing snow is relatively low cost, at least consider that option, and leave the roof as is until you can afford to upgrade.
Thanks, that makes a lot of sense. And I definitely try to clear snow off the roof whenever it begins to accumulate (originally a Vermonter so well versed in snow ). And yes, the question of why it's still there keeps coming back up. I will definitely have to consider my options carefully here.