Hey bengi3, I enjoyed your write up on the accelerator. Well done.
One thing: Allen and Torx are two quite different shapes of heads and drivers - it may be best to remove the reference to Allen to save confusion.
A better tool is a metal spudger or putty knife.
That's ... a horrible idea, and likely to lead to damage to the plastics along the seam.
For reference, here's the "official" Mac cracker, as used by authorized service shops back in the day:
[image TBA - still searching]
It's a wide spring clamp used in woodworking, often called a framer's or framing clamp, I believe. The idea is to apply pressure
evenly along the length of the seam, and in
both directions at once, as close to the direction of movement as possible. A spudger or putty knife can only apply pressure in one direction, unless you twist it - which is how gouges and chips taken out of the plastic happen.
The tool
you have here, bengi3:
... is called a "spring clamp". I presume Techworks called it a retractor because that is what it is being used for when installing their kit - to "retract" the rear of the case.
They are widely available and cheap, and come in many sizes.
This store has them up to four inches (or 12"??), and IMHO the wider the better for Mac cracking. Obviously, one removes the rubber protectors from the tips, and some advise flattening the tips in a vise as well.
This thread may also be of interest:
Suggestions for opening a compact sans Mac Cracker?