1. Find ones that fit through the hole.
2. Most LED assemblies are direct replacements for OEM bulbs, so the connector should fit.
3. For turn signals, you must buy an LED assembly that has a resistor built in. Because LEDs draw so little current, the 4Runner's electrical system will think the 'bulb' is burned out, and make it blink fast. The resistor on the LED provides a load, fooling the electrical system into thinking there's a real incandescent bulb in place.
#1 is probably your limiting factor. To produce an equal brightness LED assembly, you need a lot of LEDs, which makes the assembly bigger than a bulb.