If the “kit” says it’s “one size fits all” or similar wording, check the instructions that come with it on how to adjust it for things that are likely to vary.
Otherwise, you’ll probably need to take measurements or, if you’re lucky, there’ll be make and model numbers on the existing parts that you can use to get replacements or new internal parts.
If you’re really unlucky, you have a bizarre but genius-designed toilet made by a now out-of-business manufacturer who found novel and unique ways around patents and lawsuits and you’d be better off replacing the whole thing.
Right now, I’m leaning towards “no” on account of them allegedly being awash with money.
In the vein of alternative places to donate, consider your Fediverse instance(s). If you’re a Linux user, a few pennies towards your distro of choice wouldn’t go amiss either. (I’d also say archive.org, but someone else suggested that already.)
You may already be donating to these places, but this comment is also for the handful of other people who might see it, and like one of those arcade coin waterfalls, might trickle down into the conscience of someone who has cash to donate.