The only problem I can see with not having the radiator on hand, is that depending on who's radiator you buy, the core thickness will vary from manufacturer to manufacturer. I have a Walker in my Model A Coupe and it is twice as thick as the stocker I have in my stock Tudor Sedan. So, that would change evertyhing if you guessed wrong. I would either buy or borrow to mock up. I know I"m not much help just my 2 cents.

Keith...

If it were cheap and easy, everyone would do it.