Imagine a 26" bike with a 44 tooth sprocket. A 250 lb rider is not going to overpower that engine. That's not a problem.
Your larger wheel, of course, will change your gear ratio. To the tune of 28 divided by 26. Or 14/13. You can see that it's not a huge difference. You'll gain speed and lose torque by that ratio. A 48 tooth sprocket will counter-act this by the ratio 48/44 or 12/11. With a 48 tooth sprocket your gearing will be as near as no matter to a 26 in with a 44 tooth.
Now, are those spokes 14 gauge? I'd be concerned about that. A 28 inch wheel with 14s might be just a bit delicate for this application.
If that's the case, then I'd really recommend low speeds. Then a 52 tooth, or even larger, might be the right one.