It depends on how faulty the old pump is. The fact that it leaks does not mean that all is lost. The 617 service manual says to bleed air from the filter by loosening the union screw on the filter housing where the fuel line goes from the filter to the IP. Operate the pump until all air is expelled from the filter, then tighten the union screw. Continue to operate the pump until you hear the relief valve on the IP operate. (The relief valve will make a squirting sort of sound as you operate the pump.) Then secure the pump.
I typically find that the car is a bit slow to start evan after following this procedure.