Thanks for the quick reply.
Here's an updated list:
I added a GTX 750Ti (which shouldn't get bottlenecked by the CPU).
Changed RAM to a 2x2 DDR3-1600.
I'm not going with an SSD because my friend's trying to keep it below $600. Otherwise I'd toss in maybe 2 64GBs in RAID 0 for the OS.
My main concern with an aftermarket cooler is the case. I've got a Noctua NH-U12S that I could donate but it'd probably be too big. Maybe the Nocuta NH-L12 would work. I'd add an external radiator and do water cooling but there is only 1 grommet in the back, so not enough space for both an in and out tube. I'd tell him to just leave the case panels off but then there likely wouldn't be enough air flow over the motherboard and RAM since this would likely be tucked into a MAME cabinet.
Maybe I just need to change the case hahaha.