Thanks SO much to ralfstc, who sent me this pen, which I LOVE: from researching online, I believe it's a Waterman's 352 Stalwart, made in Canada in the 1940's. According to ralfstc, the nib was modified by John Sorowka (Oxonian).
Ralf sent me this pen in thanks for a fountain pen drawing I sent him which was in thanks for the sample of Lamy Dark Lilac he sent me. :-)
I love fountain pen people!
It's my first Waterman and also my first pen with an ink sac - I had to look up online how to use it! Any advice/tips re: maintenance welcome. :-)
And again, THANK YOU, RALFSTC! So looking forward to writing with my new pen. I've inked it up with Iroshizuku Kon Peki.