Came across some good articles on the differences between the two dynos.
Most of it was covered already, but it doesn't seem that the visual power losses were more than 10%.
Here's a few excerpts.

Absorption dynos like the Mustang measure torque and are in theory a better measure of horsepower than Dynojet The Dynojet is an inertia dyno. It calculates horsepower by measuring how quickly the car can spin up the rollers.
You cannot take a static measurement on an inertia dyno, like Dynojet. The inertia dynos are cheaper than the absorption dynos like Mustang. That is why you find more of them - less expensive.

DynoJet is the industry standard. Whatever your car puts down on one of them is pretty much gospel. Mustangs tend to read about 5-10% lower because of the roller design.
The track is the measurement stick, but as long as you use the same dyno every time, you'll know what you've gained from mods.

This deserves more explanation. Typically you will find a car that produces 200 horsepower on a Dyno-jet (fixed inertia) will only produce 180 horsepower on a Mustang (loaded inertia) dynamometer - 10% less. However as horsepower increases the numbers (as a percentage) will become closer.

 

That doesn't help me, Del.

I was hoping for something that said, "Mustang dynos are notoriously inaccurate (up to 80%!) for TBI cars."

 

What's the latest with that trans of yours Caddy?

 

i still think mustang dyno was way off judging by our crappy 1/4 mile sprints.