Just a update. I spoke to Rick at A&A transmission, and this is what he told me. The 998 electric LU has 12v applied to the single wire at the trans to lock up the converter. This is controlled by the engine computer on 88 and newer FI vehicles. The converter can be controlled at any speed or throttle position as long as the trans is in high gear (third), with that 12 volt signal. OK, now I know how it works.
Next:
I want to try and convert a slant six 904 to have this feature. Rick said I should be able to do this by swapping the 998 guts into the slant six 904 case (need to be a slant six 904 hydraulic LU trans). I would have to put a hole in the case for the electrical wire. The only thing he couldn't tell me was if there was enough room inside the slant six 904 case for the electrical solenoid. Looks very possible, so I will buy a core small block 998 LU trans.
Now the reason: I have a 64 Valiant with a slant that gets very good fuel milage. It has a 3 speed on the column. I also have a 84 D-100 slant six with a 833od trans. I'm getting older and starting to have a little trouble using the clutch. The D-100 is a candidate for a A-500 (which I have) swap, but I do not want to cut the floors on the 64 Valiant, so there for the 904/998 LU trans.
Clear as mud?