Trans Oil Pump

I feel I should rebuild my trans oil pump. I was reading some information in my trans book I got from the club. The A.S. Ayers. BTW what a great manual... I also recall Henry Portz offers an improved pump by adding a thick plate and new gears. My first question is how the drive is set so its not off center to the lower shaft in the transmission. Is there a locating pin or is it that necessary to have it positioned in line with the shaft. Also whats that glass bushing the manual talks about? Thanks for any help or ideas.