Yes the crossmember will have to move back about 2". If your TH350 has a 9" tailshaft your DS length will not have to change as they are about the same OL length. Yes you can use the linkage from the 350, but if you set it up normal you will not be able to select 1st gear. I put mine in first and set the linkage, it gets all the gears, but the pointer is a little out of line. I think to make it work correctly you need a column out of a 4spd truck.
This is how I'm wiring up my lockup circuit. All these parts cost me $65. It will be a little more if you dont have a friend at the parts counter.
http://73-87.com/7387garage/drivetrain/lockup.htm