quote from the FAQ of neons.org

The Neon automatic transmission is a three-speed, mechanically-controlled unit. Shifts are regulated by throttle position via a cable attached to the throttle body, while an internal governor sets the maximum upshift speed at 6500 rpm. It has a lockup torque converter for improved mileage, but no overdrive like the manual has. It is an older Chrysler design, and as such, is a reliable, durable transmission. The automatic transmission is not a good match for the DOHC engine, because its shift points occur too early to make full use of the DOHC's high-revving power. DOHCs are rev-limited at 6750 rpm when coupled with the automatic transmission, due to limitations of the torque converter. For people with no tachometer, the SOHC turns about 3500 rpm at 80 mph in top gear, while the DOHC turns about 3750 rpm at the same speed

the good news: you could use a high stall non-lockup torque converter made for the turbo II cars of the late 80's early 90's and they are really affordable, the tranny is also a lot stronger than the a604
parts also available for that tranny: stronger manual valve body to convert the tranny into a full semi-automatic tranny, available in reversed or regular mode, shift kit are also available

the bad news; the final ratio is 2.98 for the SOHC and 3.19 for the DOHC if you want to keep an acceleration similar to the a604 you would need a final drive gears mode, however the gears for this mod are discontinued from chrysler, howell wss supposed to do a set of 1.3 and 1.4 multiplier but i have no details or updates on this

the tranny drops in the hole and according to Glacius the axels and the engine mounts are reusable, you will need to add a shift down cable that goes from the throttle body to the tranny

Alain

one of the 2.4 true pionners