I used the scroll seal and it works fine.
Having heard all the warnings about the plastic seal setting tool, I checked the one I got, and found that the seal didn't fit it. I took it to the guy who was doing my head. When he chucked it in a lathe, we found that the two diameters weren't concentric, either. In a word: useless.
This procedure works, if you don't have a lathe to make your own seal setting mandrel. Wrap the crank journals with one thickness of Teflon pipe thread tape. Do the same with the scroll on the crank. I can't remember how many thicknesses were required there, but experimentation is easy. Put some on and hold the seal in place on the scroll. It's right when you can squeeze the two halves together, and detect no movement relative to the scroll. Once the crank is properly wrapped, bolt it in the block with the bearings, and set the seal on the block and end cap. Take the crank back out and clean off all the Teflon tape. You're ready to go.
The idea is to center the crank in its bearings, the way the oil will when it's running, and center the seal around the scroll. The Teflon tape is an easy way to do that -- and it's cheap! If you get a little too much in the bearings, it will just squish like plastigage - but all the way around the journal, holding the crank centered in the bearing.