How do YOU assemble loose cells
I too have the older DEANS Jig and had to cut off the rail from one side. The newer versions have been changed to work with 3300's.
If you have plenty of room on the sides of your Chassis, any brand of battery bar should work just fine. Some brands lay flatter on the cells and offer more clearance when up against tight chassis rails.
When soldering, hotter is better. You want to be able to complete each joint in a few seconds to avoid transfering too much heat to the Cells and possibly damaging them.