Thread: th350 to th400 swap

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With no equipment other than a hacksaw and a welding shop somewhere in town, here's how I'd proceed.
Mock up the trans at the proper angle (0 degrees down bubble on the carburetor pad on the intake manifold). Use wooden blocks under the end of the tailshaft, leaving room to bolt the crossmember to the trans mount. Hacksaw the stock crossmember into 3 pieces, cutting it so as to leave an inch or two beyond the trans mount on either side. Make sure there are no other components on the car that will be in the way of the spacer plates you are about to make. Bolt the short piece onto the trans mount. Bolt the two side pieces to the body. Using a 3" wide strip of cardboard, cut two pieces of cardboard to the correct length to connect the 3 pieces of the crossmember together. Mark the outline of the outside pieces and the center piece of the crossmember on the cardboard spacers. Take all three pieces of crossmember and the two pieces of cardboard spacers to the welding shop. Have the operator cut or grind off the edges of the center piece or the outside pieces of the crossmember by about 3/16ths of an inch so that the spacer plates will be parallel with the centerline of the car and will look good. Have him fabricate two spacers made of 3/16ths thickness steel plate, 3 inches wide to match your cardboard spacers and tack weld the whole mess together. NOTICE I SAID TACK WELD. Take the new one-piece crossmember home and try it for fit. Any adjustments can be made pretty easily by grinding off the tack welds and re-positioning the pieces at the shop. Keep doing it until it fits properly. Then have the welder finish welding it , moving from one place to another on the crossmember so as not to warp the piece with too much heat in one area all at once.