Finished. Made a correct Y55 topper and turned out really well.

Started with an R59 battery topper. Ended up being the correct size that works with the current modern offering of the reverse polarity battery. I switched the polarity designations with careful sanding and some JB weld. Repainted it and added the yellow accents. My wife is currently making a correct sticker for it based off a picture I have of an NOS Y55 battery.

Pretty happy with the results.

Just another update,

While my wife was working on making a Y55 decal, she stumbled upon a place that actually sells reproduction Y55 decals complete with warranty sticker, tag, and I guess what looks like yellow stickers for the caps and Delco script (I already painted mine) $9 I figure how easy is that? Saved her the trouble, so I ordered a set. See what that looks like when it gets here.