What year and what do i look for to find one to go behind a carberated 340?and what do i need to get to make it work? Will a 727 convertor fit it? Does it use a kick down cable? Thanks

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)

my 94 Ram 2500 still has the RH version in it...

Think all the OD versions are lock up so the 727 converter is not going to work.

No... I have a non lock up one right now.. its
from the early version

Not all were lockups. The diesel version from 91.5 to 93 were not lock ups. There were also some gas versions that weren't lockups depended on the GVWR of the truck it was in, but they are pretty rare. You can convert a lockup to a non lockup with the correct input shaft and reaction shaft. I would also use a non lockup valve body, then the 727 converter will fit.

What body are you planning on putting the 518 in? There are significant fitment issues with A bodies in the cross member area. E and B bodies aren't too bad.

If you want a non lock-up, they will be the early 2 pin ones. If the plug-in by the kick down and shift selector levers is a 3 pin, then the tranny is a lock-up.

The non lock-up 518s will use the 727 converter, the lock-ups cannot. And you will need the kick down linkage unless you use a manual valve body.

Do a search on Google on installing a 518. Plenty of info out there.

88-92 are non lockup (two wire), and 93-95 (three wire) are lockup for the gas A518/46RH, 96 and up (big multi wired) are electronic governed and lockup. 518s use the same converters as 727s, 24 spline non-lockup and 23 spline lockup. Stock 727 kickdown linkage can be used in most swaps, though some will need a cable setup. If you have floor shift a few people have successfully made brackets to run stock shift linkages, and some have converted to cable setups. The big deal is the trans tunnel, you will need a custom trans mount cross member and may need to cut and re structure the torsion bar cross member, there has been some success trimming the reinforcements on the overdrive housing to clear stock E&B body tunnels. You will need a shorter driveshaft (727 yoke). The cooler lines are 3/8" instead on 5/16"

As far as controlling it, it can be as simple as a switch or as complicated as an electronic controller. Many early conversions used floor mount high beam switches. http://www.transmissioncenter.net/dodge.htm has an inexpensive way to control it automatically. There are also a couple of control modules, but they are expensive and painful to set up.

I'm putting it in a 34 Plymouth 2 door sedan cross member is not a issue

This site has some good info
http://smrtrans.tripod.com/smrtransmissionsintro/id6.html

How much extra power does a 518 use over a 727? Or how much et do you loose, all else being equal

i would say about the same----there are 500's based off a 904 that lose less hp than a 518...