'''Sort of -''' [http://www.everymac.com/systems/apple/imac/specs/imac-core-i7-3.5-27-inch-aluminum-late-2013-specs.html|EveryMac] says: '''This model has a proprietary PCIe connector for an SSD'''. If the SSD is not installed at the time of purchase, ''the connector still is present and later professional or self-installation is possible.''
The problem may be in locating a "generic" version of this proprietary drive. [http://eshop.macsales.com/shop/SSD/PCIe/OWC/Mercury_Accelsior/RAID|OWC] has been among the first to offer solutions for previous Apple Proprietary drives. It's not clear to me if they have done so as yet for the iMac.
The RAM should not present a problem.
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