Eventhough it is - ?not? - recommended to do the Fluidampr with the RASP I did mine anyway. It is very close fit, but it does fit.
The close fits are:
The Fluidampr hub is thicker which pushes the RASP drive pulley more toward the fan blades. I pushed my RASP drive pulley as far onto the hub shaft as I could and still get the hex key in there to tighten the set screws. The clearance between the fan blades (engine not running) and the RASP drive pulley is about 3/16". I checked every blade and measured every blade clearance. I would think the fan blade would pull more toward the front of the truck with the engine running or the fan clutch engaged (PLEASE correct me if this is not the case) and the fan pulling air through the radiator etc which would increase the drive pulley and fan blade clearance slightly more.
My 1st edition RASP had developed a leak at the seal and DTT had sent me a 3rd edition RASP (which is a little longer in the pump casting, much better support for the shaft and has a sealed bushing). The RASP pulley fit fine on the new RASP shaft - but - the alignment of the cog belt is not perfectly straight because of the rubber fill plug on the Fluidampr sticks out about "1/16" beyond the physical frame of the Fluidampr. I wanted the belt to clear the plug so there would not be any issues there.
So the exact alignment of the belt is not exact. There is supposed to be about 1/2" play on both sides of the direct line between the drive pulley and the driven pulley so the cogs do the actual drive and the belt is not really pulling anything. With the not quite exact alignment and the necessary loseness of the cog belt there seems to not be any problem with mechanical interferance. Close - yes, interference - no.
Disclaimer - I do not do WOT's and generally allow the entire engine / drive system to accelerate normally (to me). If you horsed the engine around, and did not keep an eye on the belt tension (loseness) I can see where the belt could maybe might be able to get over the pulley shoulder which would render the cogs ineffective and the RASP would not be driven. I also generally do not go over about 2400 rpm, and if you went up into the 3000's + you could induce centripical force on the belt that could put more outward forces on the belt that could force it over the pulley flange.
However, works for me,
Bob Weis
Oh, $$, a little over $415 and I paid the shipping.