I put mine in the line from the pressure regulator. The idea is to cool the gas just before it goes back in the tank so it doesn't pick up any heat between the cooler and the tank. Also, by waiting until it done circulating around the engine the fuel is as hot as it's going to get. The hotter the fuel is, the more heat it will give up in the cooler.
I'm afraid my design will be hard to inmplement on a K100 or 1100 because I put mine in the space gained on the K75 by not having the fourth cylinder. It can be done, but you probably won't be able to use a cylindrical cooler like I did.
When looking for a cooler to use, avoid the radiator type coolers with thin walls. They are too flimsy to be trusted containing a flammable liquid. In my design, that is the reason I used an extruded cooler body with heavy welded ends. Try to find a cooler with the largest internal volume. Volume translates to residence time, and the longer the fuel is in the cooler the more it will be cooled.
