I just finished-up the two antique heating grates last night (for the Office and Living Room). The new casting for the missing latch was brought back to me this week, and I painted it over the past few days (primer, followed by black on the back end, then white on the front). And they are now installed and functional again.
The casting ended up being quite expensive (nearly the price of buying an entire salvaged grate), but I had never gotten an actual quote for the casting, and it's over and done now.
I wanted to share photos, but I forgot my camera at work, so I will post those next week.