Yes, texasblake is a good source for Porsche information. Read all the topics on the 951 page.
You have a 1988 924S. It has the spring tensioner as well as the slightly higher compression engine. The spring tensioner is not automatic. It gets close and you have to finish with a guage. In a year or so of serious doubt on whether you have done it right, you will be able to do it with the twist method or my favorite the thumb and water pump pully test--not now.
If you do not do it properly, the chances of bent valves becomes reality. A shop will charge anywhere from $90 to $150 to tension the belts. There are a few other options, only if your skills are good and fear is managed
You should have the upgraded waterpump and rollers. You can tell by a shinny belt guide bolted on the WP. This will help you get the correct rollers if you decide to replace.
www.Clarks-Garage.com is another excellent source.
GL
John_AZ