I've seen one of their mandolins, not a mandola. As part of an antique instrument collector's group (banjo collectors), discovering who actually built what can be a nightmare. Many, many labels (like Leland) were outsourced to jobbers. You would have to find the Leland order books to discover who actually made them. I've seen Larson, Lyon & Healy, Ditson and others named. AFAIK, the documentation is simply missing...therefore guesswork prevails. Sometimes you get lucky and find advertisements in period trade publications that mention, "so-and-so is now building a new line of instruments for Xxx." Famous trademarks got traded around like so many baseball cards.
In any case, the Leland mandos appear to have a reputation as excellent instruments, well worth bringing back to life. They're flat-back, which was a response to Orville Gibson's designs at the turn of the 20th century. Vega, Martin, L&H, Leland and Weymann (others as well) all tried to cash in on the design, probably because it was cheap and quick to build.
I have a Flatiron Mandola that I ordered from the factory back in the 80s. It looks very close to your Leland. Plays great, sounds amazing. I hope you can get her up and running!
BTW, Flatiron recommended the following string sizes for my 17" scale mandola:
1st: .012"
2nd: .021"
3rd: .032"
4th: .049"
I might drop those down a couple of thou' due to age, etc. Tuning for mandola is CGDA, just in case.