I'm not a mechanical engineer, but that crossmember connector design does not look to have the kind of support required along the lateral plane.
I am envisioning the bolt heads eventually shearing the metal of the stub end of what is left of the crossmember.
Your 1/8" plate steel should be able to withstand the shear forces inherent to this design, but the original crossmember steel is not as durable as plate steel.
There is a lot of support needed in this area because the spring perches are located in that vicinity.
Personally, I am not so sure that your design will provide that support.
