Went ahead and gutted it. Followed the procedure posted by Chick. Only thing I didn't do was protect the top as well as he did so I ended up with a few scratches. But then probably pretty normal for a batter that is probably 40 years old.
I drilled through the 3/8 threade holes for the side posts and just threaded them all the way through. I used 00 cables (probably overkill, but I will never have to worry about them not carrying the amperage. Used very short 3/8 standard thread bolts to attach the cables on the inside. Made sure they would not interfere with the outside bolts from the side post cables.
Used a Braille racing lightweight AGM and just mounted it upside down. It is way more powerful than the original battery. I have the exact same battery in my 69 Opel GT, and it doesn't lose a charge even when sitting for a month at a time without a tender. I had read that they do not stay charged well when not driven regularly, but that has not been my experience.
After shooting these pics, and before attaching a bottom plate made from polycarbonate, I stuffed some more hard closed cell flexible foam in all the nooks and crannies, just so it wouldn't rattle around.
I glued some paint sticks together to make sure the battery stayed in place, then attached the bottom plat with epoxy.
Pretty pleased with the results. And it sure is easier to put in and out because it is much lighter.
