I have a 1994 Dodge full size van with a 318 engine and an A518, 4
speed (with overdrive), tranny. I've had this van for a few years and
it has leaked fluid and made a little noise since I purchased it. I
made the mistake of putting some transmission additive for "high
mileage" transmissions. A few days later the tranny would not work. I
dropped the pan, changed the fluid and filter, adjusted the bands as
per manual. I drove it around 10 miles and the tranny started sounding
like metal grinding, very loud. I immediately took it out of overdrive
and the noise went away. I've drove the van without overdrive for
several weeks. Recently I backed off the kick-down band adjustment 1/2
turn. I test drove the van and it shifted smoother, but the overdrive
still made a lot of noise. I also looked at the electrical wiring to
see if anything looked loose. I let the van sit a few hours and the
tranny would not shift out of 1st gear.

Any idea as to where I need to look first?

I also have a 1989 tranny, I think it's a A998/99, that I would like to
use temporary while I work on the original. What problems will I
encounter outside of finding a drive shaft that will fit?