Another measurement I had to check to assure my DYAD clutch would work in my application was the clutch finger position in the overall assembly along the transmission input shaft.
The spec sheet that came with my clutch gives a very accurate measurement from the crankshaft surface on which the flywheel mounts to the fingers.
It was necessary to add the distance that the flywheel mounting surface protrudes from the engine block surface that the bell housing attaches to.
If the engine was out of the car that would be a very easy dimension to get.
With the engine in the car I could not get a caliper or ruler in position to get a good measurement.
I ended up just using various size drill bits as "feeler gauges" to determine the size of the gap between the bell housing mounting surface and a bar held flat on the flywheel mounting surface as shown in the pictures.
People are more likely to have drill sets with lots of letter and number sizes than a set of plug gauges.
It's really easy to measure the actual drill shank diameters with a set of calipers once you find out which drill was barely too big and which one was slightly too small to fill the gap. I feel confident that I got a measurement that is accurate within about .005", which is plenty accurate enough for this particular task.
Just trying to share simple, low cost ways to get good measurements for people who do not have shops full of high tech equipment or a lot of extra hands available to help all the time.