Just to follow up on my last post, in case anybody else ends up modding their BS611 to have digital temp control and a second heating element...
I ended up using a piggyback spade connector on the red wire from the control box to the AC OUT connector, and attached the OUTPUT wire from the SSR.
This way, if the SSR is set to a low temp, but the user wants to adjust temperature with the dial on the front of the Bradley controller, they can. If they want to control temperature digitally via the Inkbird, leave the control dial set to low on the front of the Bradley controller, and set the desired temp with the Inkbird controller.
Pretty happy with how mine turned out. Need to add a fan now to help push heat around!