Open it up, many late MDA screens had an oscillator and pot adjustments, a few ram at 15khz as they weren’t intended for MDA
It wasn't uncommon for late-era digital mono monitors to be dual-standard and support either MDA or CGA, but when I say "not uncommon" I wouldn't say "common" either, and it seems pretty unlikely one included with a typewriter would be particularly "fancy".
If the monitor in question is a Smith Corona HRM2 it's spec'ed as MDA frequencies, and a photo of its connector plug
I found on eBay shows only sx wires, which indicates it doesn't support CGA. (It only has the pins for HSYNC, VSYNC, Intensity, mono video, and two grounds; notable in their absence are R, G, and B, which are present if the monitor is one of the CGA-emulating variety.) I've also seen pictures of these monitors displaying video, and it's definitely not NTSC frequency.
While it's certainly *possible* with enough fiddling that you might be able to beat this thing down to accepting NTSC frequencies it's not going to do it without some hurting.
Assuming you *did* go through the trouble to do that then... *shrug*? Looking at
this it looks like the expansion plug doesn't have separate horizontal and vertical sync signals, only a combined composite sync. You'll probably need to separate that to drive a monitor of this type. Once you'd done that... it might be as simple as hooking SEROUT to the video in signal? (Although... maybe you'll have to combine that with combine that with VIDD7... and maybe WNDW* to get a fully sensible output?) The result will be simple mono, no shades of gray.
There really isn't much to be gained here because if you have the color killer enabled the mono composite output from a IIc will be almost as clear as a digital out if you feed it into a monochrome NTSC monitor.