Complex sentence: The finely carved frame of all'antica foliate decoration frames a number of the grave-slabs on display, suggesting they were pre-carved and kept in stock, and retrieved when a worthy soul like Charles Reynolds presented.
Split into simpler sentences: The finely carved frame of all'antica foliate decoration framing a number of these grave-slabs. This suggests the slabs were pre-carved and kept in stock, and retrieved when a worthy soul like Charles Reynolds presented.