tc_1:

If the picture of the pump which you have posted is of the new pump, it would appear that the drive flange (where the pulleys and fan are attached) is unusually thick. A short pump body assembled with a long shaft and a thick flange would be the same length as a long body pump with a thin flange. The overall length from mounting flange to pulley flange is the critical dimension; it should be the same for both the old pump and the new.