Need advise on settings & software to encode avi to anamorphic widescreen dvd

I got some really beautiful .avi to encode to .mpg and author a DVD...
I want to create a anamorphic widescreen....what's the best settings to use?

The .avi will need to be joined, they are currently

688x288

FAR & DAR = 2.389(43:18)
PAR=1.00
23.976 fps
AC3 audio

Basic, whenever I encode to a basic 16:9 I get a sick..fat looking 1.78:1 widescreen, and this movie will only look good 1.66:1 at most..In fact, 20:9 anamorphic? Is there a trick to setting this up?

I really don't want to force this into a generic 16:9...I was thinking of using TMPGenc and 'center maintain aspect ratio' is there tools which I could use that would actually fix the header dat to do the stretching?

Ok, this film was originally shot 2.35:1 and I want to preserve that.
Strike that...it's original 2.39:1 Cinemascope

 

You should provide more details.

What encoders have you tried?

One of the VirtualDubs should join them, either Surround or MP3 freeze would be a good bet. AVI-Mux GUI should also join them, and help fix any sync issues. If GSpot shows the correct AR ConvertXtoDVD should work and as a side benefit it uses pulldown when converting to DVD spec.