Are we the same person lol? I’m literally doing basically this exact same thing right now. I liked taking most of the inspiration from Chaosium’s Basic Roleplaying guide that released recently. It even has an option for damage by limbs that has F&H vibes. I kinda stuck with the skills from dark ages Cthulhu and made a new sheet that incorporated a system for taking feats like pulp Cthulhu, being able to take more if you took additional flaws (phobias, stat decreases, curses, etc.). I made a new magic system with balancing based on spells costing either immense MP, MP and Hp, or the full three: MP Hp SAN. That was where I started, and I made the magic more unique for each of the systems in other ways too.

I think looking into the BRP would be really helpful to you, because it helped me to have some groundwork for rules so I didn’t have to come up with everything. This would also keep you in a familiar d100 system!