As I recall from an interview I read, Felix's first EB-1 was stolen pretty early on in Mountain's career. Other than Woodstock, which was only their fourth gig(!), I think every other live photo I've seen has been the re-issue. So I strongly suspect that if he was indeed using an EB-1 in the studio on Sleighride, it was the newer one.
I'll try to dig up that interview.
/rick
btw there are two Mountain tracks in the 40th Anniversary Woodstock DVD Box set, on the bonus disc; some cool, rare video of EB-1 #1