I'm sure it would be tough. But if you do the full series, it's "only" 300k more than a 1200k, and spread out over a week, so you'd get several full nights of sleep to recover during it.
There is a "brevet week" in Iowa that I'd like to try, but I don't know if they run them outside of PBP years. There's been some turnover in that club's management, so it's hard to find info on past events.