The Indy roadster is actually a great form for a kind of indigenous "Locost" concept. All types of engines and running gear were used in that era, so there would be great freedom to innovate.
Lonnie, the reason i chose to investigate an indy Special is for those very reasons. If you do a Ferrari replica it will have to have to be red and have a V12 or people will sneer at you and applies to many other replica choices, blue for a Talbot Largo, Green for a Jaguar C Type etc. - however, if you do an Indy Roadster replica the World of engines and colours is at your feet, especially the colours, greatly varied and very exciting!
I have my Indy Roadster 2 seat tribute car all finished in 3D and we will see which way the wind blows this year ...