Which motor is this - is it a magnum or an A engine - there is a difference in heads and intake and the switch over happened around this time, so make sure you get the right thing. Converting the motor to a carb is no problem. Multiple suppliers carry cams, intakes, carbs and distributors for the motor. Many of the old A engine parts work on the newer magnum blocks. Just make sure you get the right intake - the bolt angle on the magnum is different from the older A engines.
As for the tranny, I have a 5.9 in my 2001 Dakota with the electronic tranny. Mine had an electronic valve body that I replace with a hydraulic one. I still have the lock up converter and OD, and run them off of one push button on the shifter. Around town, I run it like a 3 speed. On the highway, I shift it into OD and it locks the converter and puts it into OD. I have seen people put a series of pressure switches to do it more eloquently, but mine has worked like this for around 5 years. The folks at SMR transmissions in Canada helped me get everything working, and rebuilt my overdrive to take the extra torque of my new motor - this is a weak link on the Mopar tranny. Based on your year, I think yours should be a little easier as I don't believe they had the electronic valve body in 1990.