Thought I'd share my cook and opinion on the results.
I've done baby backs dozens of times but this was my first shot at spares.
I cut them up St. Louis style. From what I've read, my plan was going to go an hour longer than I normally do baby backs.
I threw them on for 3 hours, then foiled for an hour, then another 1.5 hours out of the foil for a total of 5.5 hours.
Meat stuck completely to the bone when biting off. They were good but under done for my taste.
Next time I'll spend more time assessing the doneness, instead of just taking them off, cutting the all up and eating them!