Match in line 7 from data1.txt with line 6 from data2.txt:
word word word six    6 1.2 -2.3 fig     six seven eight nine
word word word six    6 2 -2.3 fig     six seven eight nine

Match in line 3 from data1.txt with line 7 from data2.txt:
word word word seven  7 1.2 -2.3 lemon   six seven eight nine
word word word seven  7 2 -2.3 sour    six seven eight nine
Note: Tailing word mismatch in previous pair.

Done.