360 takes a motor mount on one side that had a slightly different spacing to fit the block. Driver's side? I forgot which one.
Converter needs to be from a 360 which comes with small weights welded on. You can also use your neutral balanced 318 converter if you get the proper 360 LA B&M flexplate which is counterweighted.
If swapping converters around, make sure any replacements are for the same trans - lock-up converter or standard. Transmissions with lock-up converters have about 3/4" of the transmission shaft tip machined smooth. They don't interchange.
If the 360 oil pan is in good shape, you won't have to worry about it. But if not, 318 and 360 pans don't interchange because of the rear seal size.