Notes:
The obverse die of this variety was also used on:
1787 Vlack 13-87CT 
1787 Vlack 13-88CT

The reverse die of this variety was also used on:
1778 Vlack 12-78B

Attribution points:
Only two 1778 reverses exist in the Machin's Mills series: 78A and 78B.  On the 78A reverse, the staff points to the 7 of the date; on the 78B reverse, the staff points to the 1 of the date.  Also, note the position of the small "tree" relative to the A of BRITAN.

Great Britain did not strike any Halfpennies in 1778.

Images courtesy of Jack Howes

Sources and/or recommended reading:
"Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins" by Walter Breen