Hi Rob,
Welcome to the forum. I do have some experience with ERA, but I'm in Australia, so there will no doubt be many others closer geographically to you who will have much more relevant information.
A thread on this forum that will give you quite a lot of information about ERA's cars is....
Superformance VS. ERA
Best of luck with your quest. If you still have a year or so before purchase, best advice is to seek out as much information as you can; talk to as many owners and builders as you can find; sit in as many cars as you can find too.
Also, look into the differences between the 427SC, the 427 roadster (no stripes, no side pipes....[only] slightly more discreet), and the 289 variants - the 'slabside' and the 289FIA. Think a lot about colours too, as that is something that you need to get right if you are build one or have one built.
Oh, and
ask questions. Don't forget that the only stupid questions are the ones you don't ask. There is a huge knowledge bank available here on this forum.
Good to have you on board!
Cheers,
Glen