Hello,
1/ A new OEM wastegate uses a spring rated to open at a pressure of 0.4 bar.
2/ I can only comment on the later style cross pipe, but the easiest way I have found is to remove the front elbow at the wastegate inlet, then loosen the two rear bolts on the flanges of the outlet pipe of the wastegate going back into the main exhaust then sliding it out frontwards together with the wastegate. If the wastegate was never removed there is a 100% possibility that the studs will break off from having turned into very rusty bits over several decades, and the holes will have to be cleaned and retapped to be used with new bolts. You do want to use stainless steel bolts instead of studs & nuts when putting it back together. In fact, PET mentions 4 replacement bolts for connecting the outlet pipe to the wastegate.
3/ The early style wastegate as found on most of the 220hp cars feature larger cooling fins than the wastegate as found on the later 250hp cars. Makes no functional difference and both style can be swapped.
4/ See 1/
