Upvote:2
Depending on your mobility (physical, amount and weight of luggage) it may be that the faster way is to use the stairs (Some platforms have escalators). Salzburg Hauptbahnhof is not that big and every platform is accessed from the underground "hub". Waiting for the lift may cost you more time and they are not that big, so it is entirely possible that the elevators will be full and you have to wait for the next one.
Secondly, if you are really tight on time, don't bother finding the right coach. Just board any coach and walk through the train until you find the one you have reserved seats. (or just use empty seats if they are more convenient to you). Once you have boarded the train, you can always ask a train conductor to point you in the right direction.
Edit:
As it seems I have misinterpreted your reason for asking about the locations of the coaches relative to the platform, let me repeat: Salzburg Hauptbahnhof is not that big. You can go from one end of the train on the platform to the other in about a minute, if you pace up your strides. There are two stairs on each platform which means you will have to go a maximum of about half of the length of the train to reach them.