I'm following in the footsteps of a bunch of 6.2 diesel swaps and will be welding up a "flex plate sandwich" consisting of the huge GM diesel one and the smaller LR one (complete with torque converter mounting holes). But when I look at plates on eBay some seem to be a single unit and others appear to have a thin metal intermediate plate with the tq converter holes on it. How does this all bolt together?

 

A Flex plate is bolted to the torque converter as you already know , it looks looks a giant gear wheel , the sole purpose of a flex plate is for starting the motor ...

When you turn your key , activating the ignition , this sends power to the starter motor, the started solenoid sends the starter gear forward, onto the gear of the flex plate turning the crankshaft to start the vehicle ...they can be around 10 mm ,15 mm etc etc different thickness's and different gear teeth (rounded , pointed etc )

if you have a worn flex plate , you will get a loud metal grinding noise on start up , once maybe twice , until it finds a spot to mesh.

the flex plate "sandwich" you are talking about , could mean that the starter does not have the reach required to meet the gear ,(since it's a conversion ) now since you cant move the starter motor forward ...you bring the flex plate back instead , and because of the term "flex" the plate is usually light and looks ,,, or may appear to some as week ..it is really quite strong and flexible at the same time to allow proper gear meshing at all times of start up ...

so rather than put spacers between the converter and flex plate , just weld another one exactly like it together ,and you are just as good as original...literally

hope that helps ..