That was indeed a huge problem with the all-wheel-drive Astro Van because it used a solidly locked full-time transfer case. Turning a corner put stress on the tires and the transfer case but that didn't last very long. Mismatched tire sizes puts the same stress on it continuously and could lead to a failure of the transfer case. If I remember correctly, yours is not full-time. If you normally drive in rear-wheel-drive, the mismatched tire won't be a problem but you must also consider the anti-lock brakes. When the tires don't rotate at the same rate the traction control system will kick in and you can get false ABS activation when stopping.

Measure the circumference of the new tire and compare it to the old ones. If there's a significant difference, it's best to go with four identical new ones.