Of course, this is not to say these are the only possibilities. In general the position of the tomb near a spring isn't a terribly helpful identifier, as it seems this is reasonably common. Jones* (p.14,26 and throughout) quotes a large number of tumuli and uncovered dolmen near springs regarded, at least in later periods, as holy, and gives references and examples suggesting springs were sacred prior to the christian period. This is also commented on by Field* (see also this Note on the age of Wormelow Tump; it is not apparent what level of statistical investigation has been completed on this relationship).
While the name "Gamber Head" is indicative (see Note), even within the area around the spring there is another village called Turkey Tump, suggesting an alternative site (in fact it is not a great deal further from the Spring than Wormelow Tump). However, no map shows a tumulus there (though there is a late chapel), and it is not clear whether the term "Tump" also applies locally to features which are apparently natural - either because it is an appropriate name for them, or because of a mis-identification of such natural features as the burial mounds of heros (for example Coles Tump (Visit Details) is a natural feature, the naming of which may be relatively late*, however, the "Tump" part of the name may be mythological, or, indeed, synecdochic as there are earthwork features on the summit* that might be (mis?)interpreted as burial mounds).
A very strong third contender must be the Tump at St.Weonards (Visit Details). While current O.S. maps show this as a motte (castle mound), older maps mark it as "Tumulus" or "Tump". It is, in fact, a large burial mound reused as a motte - it was opened in 1855 and two burnt burials found*. The original mound was remodelled and reused as one of a series of (Saxon?) defensive mounds spread along the border. Generally such mounds finished up 100-200 foot round and 30-35 foot high*. The mound at St.Weonards is currently ~45 yds (41m) in diameter and 14.5 feet high (4.4m)*. The mound lies pretty much between the two most likely sites. Although the name sounds Saxon and isn't in the Domesday Book, which might suggest this could be hiding a lost Welsh name like Landmore (see Note), it may be derived from the Welsh St.Gwennarth*.
Finally, the 1:2500 1st Edition O.S. map for Gamber Head shows something that may be a mound some 70 metres or so west of the spring on the other side of the road.