As
@fantastic noted, IPC was acquired by PremiumGuard. I used to buy 6 packs of PremiumGuard off Amazon, then started buying MicroGard Select as needed from my local O'Reilly's. I recently switched to Pentius UFXL after stumbling across a post here for cheap cases off Amazon. They are made in South Korea, & look just as nice as the PremiumGuard Extended Life inside & out. Thick textured can, silicone gasket & ADBV, coil spring bypass, big center core holes, bottoms come with the plastic shrink wrap to keep dust out, plus the box & their website state 99% efficiency @ 20 microns for 10k miles. Which I'll take with a grain of salt, but the filters look beautiful. I bought 2 cases/sizes for under $60 each. 12 filters/ case. I'm good for a few years. Here's a link for the 3600 size that should fit your Mustang
@KCJeep for $55 if you were interested.