you could mount your hdds above the PSU; an 18" cable should reach just fine (at least it does in my case; i have the AOpen HX08, which is very similar to the Inwin Q500). plus that blowhole will help cool the hdds.
to mount a heater core is simple, just get some thin bolts that are 2 1/2" long (i got mine from Ace Hardware, as Lowes or Home Depot didnt have any the right length. its also cheaper at Ace Hardware as well). thread the bolts thru the rad, and bolt to chassis.
for the res, you could just use a
weather-proof electrical box. check in you case; you might be able to fit a heater core at the lower front (thats where i mounted mine). the heater cores DDen and Dtek Customs sells measures 6 1/8" by 7 1/2".
to ECU: WW is certainly not a "fix-all", but it was specifically designed to prevent corrosion in engine coolant systems, many of which have different metals for the various components (most, if not all, car rads are made of aluminum now)
