I have a 57 Skyliner as well as 56' and 57' Thunderbirds. I dislike corrosion and would like to try an Optima battery in my Skyliner and the T-birds to prevent corrosion and because the Optimas offer quite a bit of reserve capacity. I can find group numbers for 58' Skyliners of a group 34R and a 27F on Optima's website but not for the 57' Skyliner. In looking over the dimensions, none of them really fit perfect in the Skyliner. Has anyone tried an Optima in their 57' Skyliner? If so, which group number in the Optima line up seemed to be the best fit for the 57' Skyliner? I realize in the Optima brand there may not be a perfect sized. But I'd also like it to not be rolling around either. any assistance or guidance on this would be appreciated.