Battery E36 track car

The Interstate battery in my E36 M3 has gone to the great beyond. I see lots of people talk about the Optima Red batteries but the Optima website says they don't make a proper battery for an E36. Which model have people been using? I also see lots of billet mounts on eBay, just want to make sure I get one that will fit the battery I buy.

THanks.

Battery E36 track car