Not familiar with the difference, from the serial number it is from 1970.
From the following web site:
http://www.antiquecameras.net/leicamlenses.html
35 Summicron F2 Type 1 (M2-Chrome) $ 1,800-$2,300 1,640,000 - 2,316,000
35 Summicron F2 Type 1 (M3-Chrome) $ 1,000-1,500 1,640,000 - 2,316,000
35 Summicron F2 Type 1 (M2-Black) $ 3,500-4,700 1,640,000- 2,316,000
35 Summicron F2 Type 1 (M3-Black) $ 3,250-4,500 1,640,000 - 2,316,000
35 Summicron F2 Type 2 (S7) $ 950-1,250 2,316,000 - 2,874,000
35 Summicron F2 Type 3 (E39) $ 875-1,150 2,316,000 - 2,874,000
35 Summicron F2 Type 4 $ 1,500-1,900 2,970,000 - 3,731,000 Price keeps rising - used to run $ 800
35 Summicron F2 ASPH $ 1,650-2,150 3,731,000 - Current
Find some pictures of the 35 Cron here:
http://kenrockwell.com/leica/comparisons/35mm-summicron/sharpness.htm