other than the od unit, those transmissions are like a 727.
if it were me [and in time, it will be] i would get an ATSG service manual [ i have one for the A518 and one for the A500] and a FSM for whatever year your transmission came from. [i also have one of those]
also, get the monroe book. that has very good tricks and tips in it.
then, i would obtain a good core, [i have already obtained two] rebuild it over the winter, then install it in the spring.
if you have rebuilt a 727, you can do an A518.
this is just me speaking from my personal experience over 55+ years of playing with this brand.
i'm still stupid, and i still ask questions because i either forgot or never knew stuff in the first place.
your mileage will vary.