Hi Freckles
There is this link to Manor Park cemetery here.
http://www.eolfhs.org.uk/eolcem06.htmAs you have names, dates and the plot numbers I suggest you give them a ring or email to confirm that you are searching in the right cemetery. According to the site, there is no charge at the moment for lookups, might get away with no charge as you have all the details, you just want to confirm the right cemetery.
If it isn't the right cemetery....
A map of the City of London Cemetery in Manor Park can be found here.
http://www.cityoflondon.gov.uk/Corporation/our_services/health_safety/cemetery_crematorium/map.htmTheir areas however, have number squares not lettered ones. They make a charge for lookups. But ditto above, might get away with no charge as you have all the details, you just want to confirm the right cemetery.
Tell both or either you are making a visit and don't have the time to waste wandering around looking for plots that may be in the other place.
Dawn