I tossed my Pioneer HU in the car and left the factory speakers in, fully expecting a garbage sound for the time being. Amazingly, they actually sound OK, and clearly have some sort of factory crossover somewhere. I've got the HU cut @80hz (nothing below 80 goes to them) and they are fully coherent at loud volume, and sounds like it has separate tweeters. Kinda surprised tbh. Definitely not standard Ford speakers, though the rear deck speakers are not connected atm. Have a feeling they are Alpine-made as they have Made in The USA stamped on them near the factory Ford markings.
Such an odd combo though for factory fare, a mediocre Alpine tape head unit, an early DSP (it worked), and I'm guessing 8 speakers. Guessing not many got this? Was there a CD deck variant with Alpine labeling? More of a curiosity than anything else.