This is from memory. My AGM was 64 lbs and the flooded cell battery it replaced was 58 lbs. Maybe new construction techniques made lead acid batteries more efficient, requiring less lead for the same performance?

Don't understand why your battery is 1" shorter. I thought the H8 spec defines physical as well as electrical parameters.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked