You have quite a few things to consider here like seating, comfort, style, etc.
I did a simple image search on yahoo for street rod limo. there was a fat fender limo that was pretty slick! But you need to get inside some of the vehicles you are considering to see what the interior is really like and could be as a limo. I would also consider contacting some of those limo owners in the photos.
There was a 1956 chevy super strech limo in my home town, it was pretty dar cool, and had tons of space inside. Good luck!