Hi, having been there and done it, here's my two pennyworth.
Before getting two excited about what car to do it in be very clear in your own mind what your objectives are as these will greatly influence car selection, level of preparation and all up costs.
Post or pre war ? - I note that you currently favour a open top, pre war American.
A bit of style or are you happy to do it in a shed ?
Just want to finish ?
Get a gold medal ?
Achieve a class win ?
Win out right ?
Car and preparation cost - minimum cost assuming you have to employ someone to do the work.
Just want to finish in a post war shed - $50k
Out right winner in a stylish pre war car - $250k