Hellol, i have an 84 firebird with an overdrive tranny im switching it to a turbo 350 3 speed auto matic. My question is will i have to change out the cross member?

 

The TH350 mounting pad is 2" forward of the 700R4 position. An adapter plate can be fabricated to make up the difference.

There's a kit available to make the swap easier. It includes an adapter for the mount and an adapter to install the torque arm on the tranny. Although this is a cheap and easy way to do the swap, it's better to buy an aftermarket torque arm which will come with a proper crossmember. The aftermarket torque arm will mount to the crossmember and not the tranny.

The TH350 will also need a manifold vacuum source for the modulator valve.