If you need wildly different timings for the output, you'll want the Pro, which unfortunately isn't cheap.
As for "will it capture this weird mode?" general question, it will. It does have tremendous sampling flexibility. IMHO the main selling point of the OSSC.
I've been using the OSSC to upscale a 50 Hz RGB signal (SCART) to 1024x1024 (256 lines duplicated 4x). Both my HDMI capture cards happily accept that resolution with the right software.
I haven't tried the OSSC Pro, but the Retrotink 4k should probably also work fine and is really easy to use. A bit on the expensive side though...
I already wouldn't touch the retrotink simply because it isn't open hardware, but it also is not anywhere as configurable; It's meant for non-techie people who want to be abstracted from the details.
Definitely easier to use, but nowhere as flexible.
I do not find the Retrotink 4k any less configurable than the OSSC (non-pro, I haven't tried the pro). Note that the 4k is nothing like the 5X-Pro which is more plug and play.
If you need wildly different timings for the output, you'll want the Pro, which unfortunately isn't cheap.
As for "will it capture this weird mode?" general question, it will. It does have tremendous sampling flexibility. IMHO the main selling point of the OSSC.