Hi Dan,
You might want to consider taking the original radiator to a radiator repair shop and have it re-cored. That way you will have the original Harrison tanks and the inlet and outlet for the radiator hoses will be correct. It will cost about the same to re-core as to buy new. I do not have any experience with any reproduction radiators.
Regarding the best place to buy vintage tires, there was a good thread about that recently here on this forum. Go to the Rims and Tires section and it will be the last post about where to find whitewall tires.
John