Try what you have now. The Ford motorsport headers are 400 series s/s and are as good or better than any others. (JBA are of equal quality)
If they are P specific, you can sell them at a premium price if going long tubes.
Motorsport P headers are what you have.
If you want to stay with 1 5/8 shorties pick your poison there are plenty out there.
If your going long tubes prepare for new h or x pipe some cursing to get them in and careful driving if your slammed.
One has to appreciate the shorty header life style.
Them long tubes hang up and drag on everything. Driveways, speedbumps, trailers to name a few. Im with you keeping the shorties. Some power gains just aint worth it.