You need to change the belt routing a bit. Don't just skip the smog and run the belt from the alt to the water pump, you need to go from the alt down to the crank around it counterclockwise and then up to the WP around it clockwise
I just got done pulling A/C and installed the Ford Racing kit P/N M-8511-A50 and bypassed the smog pump and used a 71.5 inch belt. I also have underdrives on the crank and water pump. It's really a pretty easy job, I just have to take out the piece in front on the radiator. I left the stuff behind the firewall though. I have done a heater core before on a 87-93 style and what a pain in the ass. Good Luck....
Ya know, i did this whole stupid thread with all these "key words" that were sure to show up in even the most vague of searches, with the hope that these little threads wouldnt pop up anymore....lol
If you're just bypassing the smog in combination with the eliminator kit, you can use the same belt size as if you were removing the smog. Take notice of the belt routing that's in the thread as well.