Tom
The hardware kit is the small, permanantly mounted blocks that the larger EAAK attach into. The HF-053 hardware model kit would be used BY ITSELF ONLY; the HF-051 kit would also be used by itself. You have two conversion kits for two separate AAV model kits. It is not unusual to see both versions in action, as both are a pretty common configuration, side by side, though generally not in the same AAV company, but its not unheard of or rare by any means.
Included is a shot of both types, with EAAK attached and without, sharing the same bit of real estate. I have some shots from OIF that have both with and without EAAK as well.
Hope this clears things up for you. PM with any more questions.
Stateside with AAVP7A1's with RAM upgrade, both with and without EAAK.
OIF AAVP7A1 w/ RAM upgrade but without EAKK added
OIF AAVP7A1 w/o RAM upgrade with EAAK added