Harald, I have used Gunze H80 before and it did not work well for me. NWE British Shermans could either be painted in U.S. Olive Drab No. 9 or British SCC 15, the British approximation for U.S. Olive Drab. Unless the British Sherman was reworked for some reason such as repair or Firefly conversion, it would likely remain in U.S. Olive Drab, the standard lend lease color. Tamiya’s Olive Drab (lighten a bit with XF57 or XF4 or even XF21 before use) is about the best U.S. WWII Armor Olive Drab available. For SCC 15, I use a slight modification of the suggested mix in Tamiya’s Cromwell kit; my SCC 15 mix is XF1:1+XF26:8+XF52:8.
If you still want to use Gunze, try H405 or H420:3+H340:1 for SCC 15. For Olive Drab, you could use H78:3+H340:1 to get a good approximation. HTH, Rich