What about swapping to a 518? Its just a 727 with an OD. That OD sure would be nice for gas milage.

 

for some reason I found that funny.

 

The 727 I had in my 440 Roadrunner was bullitproof but the later versions of it with the O/D were not nearly as dependable.... never understood why just adding the overdrive and instant , my wife had her 98 5.9 Ram in the Shop with the tranny under warranty 3 times and I rebuilt my own 99 5.2 after only 60k miles ( it had several real probs in it ). Neither of these trucks were raced or abused, well maintained... ( I had the roadrunner for 17 years ).
Now I have over 300 dragstrip passes on my 03 Ram Hemi along with other floggings and so far no probs. About to change the fluid to Amsol.
Are there other trannies, that they put into the bigger trucks, that would be suitable to your application? I know they put the 5.9 Cummins into all kinds of heavy duty vehicles and you may not even need an adapter.. there may not be anything suitable for the dragstrip however....
The 727 Can be built to handle the load but if you drive on the street be careful of how high a stall you put in, as I have seen more than a few of them cook the fluid in short order with a lot of street driving and high stall and not enough cooler, even though coolers were installed.
Good luck,
TJ

 

the 518 is for the smaller V8's... you'd want the 618

i wouldnt ever say any of the o/d units are a 727 with an overdrive. The 727's are good transmission while the 4 speeds are crap unless you build them up.

i've taken a few 42re's, 46re's and 727's apart and they are not the same. Same initial design, but that's about it.