Complex sentence: Delin's original decor seems to have been simple, but some of his instruments later received "makeovers", most famously his 1760 clavicytherium, that was retrofitted with an elaborate gilded, rococo door.
Split into simpler sentences: Delin's original case decor seems to have been simple, but some of his instruments later received "makeovers". Most notably his 1760 clavicytherium, was retrofitted with an extravagant gilded, rococo door.