The "indexing plate" must be something for Quicktime bellhousings. Normally the center register hole in the bell housing is used to center the trans to the bell, so this register hole is where the dial indicator plunger is placed. This is how the OEMs center the trans to the bell. If using an aftermarket bell, check with the manufacturer. Joel, you'll use the trans register hole in the bell.
The tool itself is ok, although the magnetic base tends to shift out of place unless you're very careful. Joel, you're more than capable of making a simple bracket that bolts in place using one of the crank bolts, then holds the dial indicator in place. Much sturdier than the magnetic base setup.
That video does a good job of explaining the process. It is important to torque all the bell housing bolts down every time you measure. The video says "same torque on all bolts" is more important than the specified torque for the bell housing bolts. We disagree. Bolt to specified torque, in the same sequence, every time. It is surprising how much bells, especially fabricated steel ones, will warp as they are tightened. OEM bells are better, but can still warp a little. "Just snug" will have you running in circles, chasing the offset. BTW, I'm not a fan of hammering the offset dowels in place like he shows. That's a good way to mushroom the dowels or raise burrs on them or the bell. Remove the bell, install the dowels, reinstall the bell.
Once you've got the offset dowels set and the TIR is good (and the center lock screw in the dowels is tightened to spec), loosen the bell housing bolts one last time and re-torque, and check TIR one more time to be sure. TIR </= .010" and you're good to go.
The guy in the video says that Holley / Lakewood offers a variety of offset dowel designs. They do indeed, and the best ones, by far, are the ones he uses in the video. The others tend to be too tight or too loose in the block. The expandable ones he uses in the video don't have that problem. They are also the most expensive by far. Summit sells them for $112.95 per pair.
Here's the thing: Holley bought those dowels from us (RobbMc Performance) in bulk for about $22 a pair, then marked them up to $112.95. Yes, really.
It's been a while since they bought from us, so maybe they've copied the design and are making them. We charge $29 a pair. In fact, some guys buy them from us in all 3 offsets (.007", .014", .021") before starting the process, so they can use the offset needed without having to measure, then place the order and wait for the dowels. Let's say you order all 3 offsets, then measure and find you need the .014" ones. You can then return the others to us; as long as they've never been installed, we'll refund the purchase price for the unused ones.
Finally, Joel, you're using the stock bell housing, so if you need offset dowels, it will almost certainly be the .007" ones.