Congratulations on your 'new' tenor guitar. They are really an under rated instrument, and a lot of fun. As for your intonation problem Hmmmh - When the instrument was tuned CGda, did it play in tune? Second question ... can you measure the guage of the original strings and the guages of the replacement strings?
Often the change to heavier strings when you move up (?), down (?), over to GDae will be frankly ... off a bit. As the guitar has a pin bridge ... The first thing I'd do is measure the distance from the nut to the twelfth fret. Then, on the D and a strings, measure the distance from the twelfth fret to the bridge. (The total of the two distances will give you the scale length.) The distance from the 12th fret to bridge should be the same as the distance from the nut to the bridge. #
Pin bridges are meant to be adjustable by replacing the saddle in the groove. If the saddle of the bridge has been set for C tuning, you may need to have another saddle cut to get it back into tune. The offsets for the strings (the grooves where the strings ride in) can be a bit different than for a mandolin, OM or Tenor banjo. As for the foot rising up on one side, often that can be clamped and reglued. Things that old have a tendency of sagging in the most inappropriate way (I know that as I'm even older).
Mandola fever is permanent.