First you would need to use the RH version of the
518 instead of the RE(the E is the electronic version)..
you can find 2 types of the RH.. if you look at the OD
plug located behind the shift lever on the case.. there
is a 2 pin or a 3 pin plug... some early ones had a single
pin... but you dont want the 7 pin plug... that uses the
computer to operate the trans... I have both a 2 pin and a
3 pin... the 3 pin is a OD and lock up... I changed out the
input shaft and the pump to allow the use of a 727 conv.. I
have a 727 5000 stall in mine... this will eliminate the lock
up.... I use a manual toggle switch to run the OD.. if you
leave it on, when it hits 3rd gear it will go into OD.. turn
it off and its a 727... without the lock up in it I leave the
switch on unless I'm gonna race it
EDIT
If you run a lock up conv then you have to turn that off
when coming to a stop or it will try to stall or lug... but
the lock up conv isnt strong(the lock up clutch is small) and
to get a lock up conv built with any decent stall is pricey