You would want the RH trans.. 88-92... they have
some early ones that didnt have the lock up conv
but I would still check the input to make sure
the conv fits.. those years have a plug connector
with either a single wire or 3 wire(located just
behind the neutral safety switch)... it will bolt
right up behind a 340... trans mount is different
so a mount would need to built.. the trans is longer
than the 727 so you need a shorter drive shaft.. yes
you need the kick down cable.. Locar makes one
EDIT
the 518 uses 3/8 cooling lines.. then just a toggle
switch to ground the solenoid for OD.. and a 12v power
supply to the solenoid (center pin)