I'm planning my fuel system upgrade...FINALLY..... and was not sure if the FASS retains the stock fuel filter.

I am understanding the system I want Filters and de-airs the fuel.

The stock filter housing has the fuel pre-heater so I imagine I want to retain that??

 

Your choice....you can keep it on there if you like. Really no need to though. I took mine completely off and ran the FASS fuel line directly to the VP. I've noticed no ill effects. I just add Power Service to keep the fuel from gelling.....where I work gets very cold in the winter and I can't plug the truck in there at night.
The FASS also can be plumbed into the engine's cooling system heater circuit to warm the fuel, though I've not yet felt the need to do so.

 

What he said above. I've had mine done that way for 5 yrs now.Havent had any problems at all.Also if you remove the stock filter and canister,it really gives you alot more room under there.