I can't speak for why other companies that don't make them fit perfect but as with most classic car installs, it's very common (as in this case) for an owner to choose a motor and water pump that is not specific to that car. Hence you have a hybrid of a particular car. The possible combinations are literally endless. So just like when you put a different motor in the car, there are 'things' that need to be worked out, the same goes for a radiator.
We have a direct bolt in 67-69 Radiator that some of the members here on the forums helped us design. It does fit literally perfect. However, the owner's application caused the outlet positions to change and therefore dictated a different radiator.
Overall, most owners would agree that the 'tweak' is a small price to pay for knowing you have the best cooling radiator available, has OEM style stamped tanks and that it will be the last one you'll ever have to buy. :)
