If you dont want to re-boil it you've removed enough flesh you could just re-fill the pot place the head in it and leave nature to do its job in a week or so, the hyper hydration of flesh and cartilage strips it all off with mild agitation simple as walking over giving it a twirl in the water every few days.
Its how I do all my roe inside (water changed daily) since I HATE scraping, the benefit at the very end of the day I literally have a flesh free animal there's nothing on it every bone I can see and there's no cartilage or dried up flesh inside it.
My roe are usually a little cleaner than your red doing that, but if your doing it outside it hardly matters tbh.
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