how to fit oil pump on 2001 astra 1.7 dti , y17dti?

how do i change the oil pump on astra 1.7 dti isuzu engine y17dt ive got it stripped down and ther is no locateing lug on the oil pump shaft or pulley so it jus spins loose not turning the pump. do new pumps now have a D or half moon shape shaft so the new pulleys with a D shape center sit snug so it locates and keeps there? also the pump as two bolts goin thro the bottom of the engine which is not the sump do i hav take the bottom end off? and do i need a new pump and pulley? and not just a pulley thank you.