I don't know your truck, but, if the pulley is not lined up with the crank shaft pulley, then put the spacer between the pulley and the pump shaft. Otherwise, put it between the pulley and the fan to get the fan close enough to the radiator so that the shroud will cover the blades.
The reason I say that is that my truck got a 292 from a dump truck and I didn't remove that engine, plus I put it in my 59 which never had 292s. So...I had to play with the spacers and fan pulleys till I got the mess right.
