street rod cooling

i screwd up my last post so here goes again.
question out to whoever is running a open engine compartment.
does it affect your cooling very much as opposed to a hooded fendered car or does in not make much difference?
i would assume at speed it should cool pretty good as there is just so much more engine area exposed to the airflow as opposed to the heat being held in ??
reason why i am posing this question i that i am trying to figure out what size if rad to put in my t bucket. the one out of the eldorado that the motor came from is just slightly smaller that a slab of plywod.
i would think a smaller 3 ot 4 core rad should do the trick.