Thanks MarkT. I've never seen this bike run. When I got it the lighting coil was damaged and I replaced it. I'm a retired Electronics Technician so I'm not too bad with a soldering iron and heat shrink. I'm also an old fart, so it is possible that I screwed up somewhere along the line. The points and the condenser are both new. I guess I'll tear the stator apart and recheck the wiring. It has to be there or the source coil itself.
As to the point gap, I've brought 4 of these guys back to life and setting the points at .3mm gets you in the ballpark. At least enough to run, but of course not perfectly. Anyway, I'm just trying to get spark here.
I just had a thought. I checked the AC out of the coil, but I should have done it with the points blocked open. Thing is, I still won't know what a good reading is.

You've kind of asked for the proverbial needle in a haystack. You're hoping that someone out there somewhere with a '74 DT250 has spun their engine with an electric drill to measure the AC volts coming out of the source coil. Believe it or not, I have made this EXACT video! :-)
Feel free to watch the whole thing, but the part you likely care about is here:


I saw the voltages that you were seeing at low RPM, and then up to 6-7v when spinning faster. I'd guestimate how fast you were spinning it while watching my video. I keep the voltmeter in frame so you can see it at all RPMs.
What are the odds??!!!

Great Video Scott. I did find the problem with mine and it wasn't the coil. Both my points and condenser were new so I kind of had a blind spot in my troubleshooting procedure. I had gone over the points with 1000 grit when I put them in, but when I got back to "Logical Troubleshooting" like I had learned so many years ago, I found that even though the points were closed physically, they were open electrically. A little 400 grit applied to the points and I had plenty of spark. These were NOS Yamaha points so they probably had been sitting for decades. Lesson learned.