Ironically, a radiator replacement is why I'm here
That radiator that they list in the parts book is actually for an early '90s Mercury Tracer, and it is several inches wider. When I measured out my '91, it looked like I could physically fit it in the car without any cutting, but the lines to the A/C condenser would be in the way (and I don't want to lose the A/C, despite it not even working at the moment).
I searched all day for some place that stocks the radiators we need, and came up empty handed. Napa told me that they can't even special order one, period. I ended up having Autozone order one, part number 431514. Same shape/size, same inlet/outlet, mount positions, etc, but it's copper/brass vs the stock aluminum/plastic which is better from a cooling standpoint although it will weigh a few pounds more. Living in Phoenix, I felt a few more pounds of weight for better cooling is a worthy trade-off for me.
Just ordered it earlier today, supposed to be here Tuesday afternoon, I'll update here if it works out.
If you're looking to stay completely stock, and your end tanks are still good, your best bet will probably be to visit a local radiator repair shop to have your existing radiator re-cored or pick up one of the used ones offered here.