I bought the battery for my '79 at a NAPA Auto Parts Store. As I remember, it was no problem getting a battery that fit correctly.

Kevin 

 

Majority of all our cars(C3 vettes) take a side post battery... and while originally they took a group size 74(which is physically the same size as the preceeding top post battery that GM used), the 74 is now basically an obsolete battery. The group 78 is a  little shorter, same width, and little heavier amperage.  Dont get sold tooooo hard on cold cranking amps,  our cars originally only required a 350 CCA battery(now-a-days thats a lawn-mower battery).  Look for a moderate rating, our MT-78 is rated 700CCA, which is very adequate.  Higher amperage ratings are somewhat "frivolous" unless you live in an extreme colder climate(like for instance Norsky(Minn), or Terry(Alaska)) .  Best i recall, Portland isnt what you'd call severe cold climate, wet maybe... but no 15 F days on end...  soo, dont go out looking for 1000CCA batteries, they tend not to last as well.  Other options are the SLA types(Sealed Lead Acid) like Optima batteries.  They are a good battery, but, we dont see it being worth twice the cost as a conventional.  I might even make another suggestion, get a dual terminal battery(one with top and side posts)... cause one time or another, either you will need a 'boost' or need to recharge your battery.  Side posts are such a pain to jump cause all you have is the bolts to hook onto.  well, think i rambled enough(after all, i do work for a battey distributer)... any questions just feel free to ask..

I just took a look, they are all Delcos, 3 are model "75", one is a "70" which is shorter but the same width. No problems with fit or connections. I even have the knob type cutoffs installed on two with enough room to get at the knobs.

 

I did buy a new one last summer at Pep Boys and simply asked for a Delco model 75, side posts only. The guy looked confused, wanted to look it up and I just insisted he go in back and get a "75". He figured it out.

 

The same model can come with different cranking amps and warranties, seems each of mine is different, but the case size is the same.

 

specs for a 78

Weight:	36.70 pounds
Length:	10.25 inches
Width:	7.25 inches
Height:	7.38 inches
Cranking Amps:	875
Cold Cranking Amps:	700

 

as for the group 70... i wouldnt bother, it is physically smaller than the 75 and usually half the amperage.  The 78 is more of a seller than the 75, as it has just a bit more reserve capacity however, it is more difficult to get your hands on it inside the battery well behind the seat.  One reason i would recommend a dual post battery(from Interstate anyhow) as the dual posts have handles... from other parts stores(Advance/autozone/oreilly's) nearly all theirs have handles installed...

 

good idea to store your batteries in the basement, just be sure to keep them charged. Out of the car, fully charged, you can keep them stored for about 3-4 months before recharging them.  As the temperature lowers, a battery self discharges much slower.

The 1 1/4" extra length of the 78 seems like it would be pretty tight. Connecting the cables, too. My disconnect switches are pretty tight with the 75s, but doable.

I remove and install em so often and take extra care to NOT touch any interior surfaces with them. I've seen a lot of Vettes with burned carpet by the battery box. My 78SA that I had back in 87-91 needed new carpet in the rear, only 9 years old at the time with 700 miles on it.

And all my Delcos have handles, but they're expensive! Over $100 compared to maybe $50-60 for a store brand.