Yes, I agree. I am inclined to think that likely, the rust overall inside those tubes, is probably not as bad as it may seem right now. And even with the rust inside the tubes, I would expect that on most any bike of this age, there is a fair chance some rust will be inside the tubes, simply because that was bare steel, and likely had little to no paint even from the beginning, so rust is inevitable. Since it is now stored indoors and will be maintained, its good to know that any existing rust should not really progress further. I will be getting out the hack saw and taking a look inside here in the coming weeks, so we will know for sure then.
Thank you everybody for all of your advice, and I feel that I have the information I need now to do a proper job. I'll be keeping yall in the loop, and wishing everybody happy and safe riding!