Your midplate is 1/2 inch thick????

What types of flex plate are you running, stock or aftermarket?

If it's the factory 4 point star type with cut outs in the points, you could try a solid round aftermarket one like a B&M.

If the 360 is externally balanced it would be one like this.
It would flex less than a factory one.



https://www.summitracing.com/parts/bmm-1...ASABEgLtoPD_BwE

As far as a spacer for the torque convertor to crank stub, they may have to be made by a machinist.
I did a quick search online and didn't see anything.