I am in the process of installing a 5.7 hemi and the 545 trans in my 73 duster. I had to widen and lengthen the tunnel significantly as well as fabricate a custom mount. I am planning to use the factory computer. It is definately a large transmission, but I wanted the modern transmission with overdrive to go with the modern engine.
Please don't take this as non constructive criticism, but I have been giving quite a lot thought of late to the problem of installing transmissions with too large a girth to fit in the stock tunnel and/or those that cause interference with the torsion bar crossmember.
Because this crossmember carries the weight of the entire car at the torsion bar anchors and transfers that weight into the car's structure through the floorpan, simply whacking the section out and allowing the stubs to float probably isn't the hot setup.
Rearranging and beefing up the welded on tunnel section of this crossmember seems to be the norm, along with altering the transmission mounting pad of the bolt on lower section, the main goal being to retain all, or as much of the original structural integrity as possible. All this seems to be achieved with varying degrees of success while keeping the modified structure from encroaching on the interior. While cantilevering a stout fabricated center section out a number of inches behind the original remaining crossmember stubs in the above shown example may appear to be the solution, it is probably going to result in the stubs moving around enough to affect handling and may eventually cause the crossmember stubs to tear loose from the floorpan.
As most are adding full length frame connectors, some are adding torque boxes, and most are modifying the tunnel extensively anyway, why not instead simply cut the entire torsion bar crossmember and floor section loose from the floor and longitudinals, move it back five inches (5.2 to be exact), and reweld it to the floorpan and longitudinals, fishplating the joints if necessary? Doing so would lessen the modifications to it needed to clear any given transmission and would allow the use of unmodified B body torsion bars in the A body (same hex on the ends but 41" long as apposed the 35.8 length of the A body bars). A simple transmission mount perch could then be welded onto the front of the basically unmodified bolt on crossmember section if needed (maybe not quite that simple for the monster of a transmission shown above).
While at first this seems like a more major undertaking than modifying a stock located one, the reality is it is probably no more difficult and might even be easier.
Just a little food for thought.
