Actually - you don't need to remove tension off the timing belt - the tensioner bearing is tight, so the spring in the snail mount isn't doing anything anymore. The spring that's in the Snail Mount only serves its function during installation of the timing belt (and was probably originally designed as an assembly aid for engine assembly/production).
What I do is (for removal)
- I pull back the spring and zip tie it back, this way it's not loading up against the tensioner bearing. This makes removal/installation a little easier. This is easier to do on a late model car with a removable trunk panel, as it takes a little bit of "umphh" to pull back on the spring (you're putting it into compression). Sometimes the spring is missing -
- The lower two bolts aren't too bad to access - the top one isn't easy - I use an offset 17mm boxed wrench, but it takes a while to get it out. If I recall, I used a 17mm gear wrench on the lower two. You can use the new mount to get a sense of the limited space you're working in - and you'll need to support the motor of course. I remove the through bolt first, lift the engine up a bit (a jack under the pan with some wood - not the best, but can work, or use a cross bar from up top - whatever you have, and make sure it's safe! - pinching your hand in there would suck).
If I recall correctly, the mount uses dowels - so it's easy to position - but I can't recall if that's actually correct or not.
What year is your car? If you have a 79-up, then you can remove the trunk access panel - makes life a bit easier!