318 to 360 swap

You won't have to do any welding to the 73 318 mounts. The drivers side is the only one that will need some help to fit. Mount the brackets behind the ears on the block, as always. You will see that you just need to stack up some washers between the block ears and brackets on the one side. As mentioned above, make sure you use the right torque converter for a 360 or get a B&M flexplate that is balanced to work with the 360 and your existing torque converter. Also.....a 360 LA is balanced different from a 5.9 Magnum, but both are externally balanced. If you're putting in a 5.9 Magnum, just use a 5.9 Magnum flex plate and rat one hole out so your existing torque converter will bolt up.