Hi Mark,
Thanks for writing in! Your mortise lock reminds me of the 82-211 Mortise Latch & Keeper set. To determine if this is the right fit, carefully review and compare the dimensions below.
To replace the handle set, if you are looking to stick with the wood handle, take a look at the 82-020 Mortise Style Handle Set; to convert this to a keyed lock, you'll need the 82-310 Key Lock.
The other compatible set is the 82-033 Patio Glass Door Handle Set. To convert this handle set to a keyed lock, you'll need to purchase the 82-306 in addition to the handle.
They both have a 3-15/16" installation measurement.
The price of each part is available on their respective webpages or on the bottom right corner of the images below. You'll be directed to their respective pages on the website by clicking those links.
