What civy battery group will fit in M35A3 tray?

[1 Patriot-of-many]

I did a search and came up with group 24 and group 31. I don't think they were in an A3 tray though! The A3 tray looks like it has moldings at the bottom so a 6TL won't move around side to side. So specifically, who has replaced their 6TL's in an A3 and with what? Do the A2 trays have the same molding at the bottom as the tray on an A3? Are the 31's sitting on top of that molding? I measured but with all those bolts sticking out into the tray, I don't see how a group 31 will fit.