I'd recomend just ordering a correct 8 ohm 4x10 reproduction dash speaker from turnswitch.com . Keep in mind ,The factory AM only puts out 2 1/2 watts .
It's a mono radio , so You are going to only be able to run one speaker (unless you use a factory fader switch), and you have to use an 8 ohm speaker , most if not all modern over the counter speakers are 4 ohm and will overheat the radios output transformer.

Greg