Transmission O/D advice needed

Ok folks.....I have a 1975 Duster with a 360 with an 833 4-speed with a 3.91 gear. I want to put an overdrive in it for cruising purposes. I have purchased a 518(46RH) that came out of a 93 Dakota with a 318 in it. My question is, can I use the torque converter that came with it behind my LA 360? OR am I going to have to purchase a new Converter to go with it to make sure the balance on the engine does not get messed up.
TO BE HONEST: I am trying to decide which method would be best in the long run to put an overdrive setup in the car. Seems like about 4 or 5 options would be.....
1: The 518 and the cutting of the crossmember
2: Gear Vendor Unit
3: Passon Performance A-855 to get the 5th gear
4: A World Class T-5 transmission (also cuts the crossmember)
5: Find a Late 70's O/Drive 833 and lose a gear.

I"m not against any of the work but want to make sure the vehicle will be reliable when I'm done. I welcome all feedback and any other ideas folks have.