I just pulled my chainplates after 34 years and they also looked good externally. I had new ones made of 316 which I purchased myself and had machine shop cut finish and polish. They are the same thickness - 1/4" - but longer with one extra bolt through the bulkhead. The old ones are now the backing plates instead of the thin backers that were original.
Could I have re-used the originals - maybe but I didn't want to take a chance.
1/8" thick on a Gulf 32? That definitely seems too thin.
Living aboard in Victoria Harbour