CENMATE Aluminum 8 Bay Hard Drive Enclosure with Cooling Fan for 2.5“/3.5" SATA HDD/SSD with USB A/C 3.0, Support Hot Swappable, Tool-Free HDD Enclosure, DAS(NO RAID/NAS)

You can simply run JBOD mode so each HDD acts like a folder or you can use unRAID or Windows Storage spaces to mix the drives as a store pool. You just need to evaluate the electricity cost if it makes sense to run 27/4 on the old system. You can buy an external enclosure. Not sure what your old system has - you may be able upgrade the case and add an expansion sata card. https://a.co/d/0hDTYLnz