I had no issue installing IOKP. Im running it right now.
Heres what I did:
(FYI, I use TWRP recovery)
Factory Reset and wipe System
install IOKP and IOKP Gapps one after the other
Thats it. It worked for me on the first try. I'm running 4.3 on my S4 now.
Use the most recent version of IOKP, I used "iokp_jfltetmo_official_2013-11-08"
Use IOKP Gapps and not regular Gapps.
I'll post screens soon.
Be sure to thank Jamison904 and his crew while you're there!!!
Infamous Open Kang ROM
[ROM][4.3.1][Official] Infamous Open Kang Project [jfltetmo] - xda-developers