I remember that thread.... about Optima lifespans....
Wow, the '77 used sidemounts, huh? My 75 uses top - and I will only ever buy Optimas in the future unless price is an object.
These spiral cell, almost gell cell, type batteries, of which the Optima is one of the earliest and most widely known offer a lot of advantages. They never leak and can even be mounted upside down. Even the non-deep cycle types (the red tops) tolerate a much greater discharge (repeatedly) than a standard liquid multiplate lead acid variety and are really halfway between a regular and deep cycle version of those. Another great advantage (the other one that made these an early favorite with the 4 wheeler (not "ess-yoo-vee", but
REAL "he-manly"
FOUR WHEELERS 
) crowd is they are much more resistant to physical shock.
One drawback is their lifespan is typically less (as is their peak cranking amp performance - in general) and when you approach the end of that span, they tend to drop out quickly. This can alarm an infrequent enthusiast, but isn't really a problem if you just change them a year or so before the stated lifespan or as soon as you notice even a relatively small drop in voltage before startup from what has been normal in your car (something on the order of 0.3V is cause for notice.)
A question I've always had is how heat resistant are they compared to a regular lead acid battery? If it hasn't leaked away, the liquid acid solution in a regular battery sloshing around between the plates pretty freely would seem to make it reasonably tolerant of heat, and I don't know if the same is true of the Optima types. This is not a big concern in C3's since the battery is where GOD intended - away from the engine heat and towards the rear where the weight is better put. (Some might note this auto design god had mysterious reasons indeed for not putting it behind the
passenger, but that's another topic.)
