What kind of battery are you running with a stock setup? I have a 69 510 4door that came to me without a battery. I read that a size 24 was stock, but that seems too tall - the terminals are almost touching the inside of the hood when its closed. Is there a shorter battery that works well?

@zKars

The 24F is the group that fits. It's tall, but it does not touch the hood. Close only counts in horse shoes and hurricanes.

I'm a fan of the group 51 honda batteries. Smaller, common, if you won't start your 510 you need to fix the car, not the battery. You will have to invent your own hold down of course. 

Thanks guys. I have an old 34R that came out of my 240Z, which is a fraction shorter than a 24F. I'll give that a try.