Searching for 1298723 handle

A quick learner says:
The number 1298723 is cast inside the handle. I want to make this a keyed entry. Screw holes are 3 15/16" apart. I have two doors to do this too. Outside looking in, the lock/slider is on the left. I'm comfortable making the modifications to existing hardware, just don't know what cylinder to get or if there is an additional extension piece to house the cylinder.
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Casey from SWISCO responded:

Hello,

I would need to see your outside pull to determine if you could use our 82-310 or 82-315 key cylinders.

If you'd rather replace the entire handle set and the thumb lever on your inside handle is offset, or closer to the bottom mounting screw on the pull rather than perfectly centered between the screws, then you should be able to use our 82-086 legacy handle set. Take a look and see how the parts I mentioned compare to yours and look over the videos we've related for you. Thank you!

A handy person from Seattle says:

Ive done a little more digging and I believe this is a Truth Allure Series 40.85 exterior handle.  I have two doors with the same hardware.  Both have the mortise lock on the left side when outside facing in.  

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Casey from SWISCO responded:

It looks like your outside pull has cut-outs to install a key lock so take a look at our video below that will walk you through the installation process. 

How to install a Legacy Handle Set
How to install a Legacy Handle Set
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