Here's a ten year old options list from ERA:
http://www.erareplicas.com/427/427options.pdf I'm sure the prices have gone up, but it's handy to at least have a list of some of things you might want to include. Some of the stuff that you don't think about can get kind of pricey, like a custom fit top and side curtains. Other things you can't even see and are pricey, like 6 pin hubs or a big brake upgrade. Other than options that you'd never even think about unless you thought about it for years, like a Quick Release Hub on your steering wheel (which is wonderful to have for a number of reasons), you should try and choose your options now based on how difficult it would be to "upgrade" later, should you choose to. For example, upgrading to the outboard braked rear down the road is a pretty big PITA. If you want it, get it now. Side curtains, not so much of a PITA so long as the ferrule holes are in the door. Point being, you need to think it all through if you want to do it right the first time. Now, one of my favorite things to do with my QR hub is to pull my steering wheel off while driving down the highway and hold it up in the air while screaming. It never fails to elicit a memorable response from my passenger.
