bryang -
on the aero with the manual there are two "hidden" bolts that you have to access sort of inside the flywheel cover... there are supposedly factory "punch outs" in the two spots that you can tap out (or in with all probability) with a hammer (ball peen hammer probably a good bet).
here is a thread i found on another site that has a picture a guy took of where he drilled in. in principle the drilled areas are where you need to get in. so the factory weakened punch outs should be around there.
if there are no punch outs readily observed, you can drill first in the areas with a small drill bit (pilot hole) then use a step bit to achieve the size hole you need to get your tool of choice into to work the bolts out.
you do not have to swap parts over to new parts unless your pickup tube and screen are so badly damaged that they cannot be saved. however it is highly recommended to get all new o-rings for the pickup and it's pump connection (there are at least 2 you need minimum) and give everything a really good cleaning and put it back together and do your reinstall.
EDIT:
much better picture of the punch outs already removed on a car:
http://uksaabs.co.uk/UKS/viewtopic.php?f=2&t=81540
img