Need help for engine identification

You need to look at a different number first. Stamped right under Plug #1 (the one you are showing in the picture). I can make out the digit 4. Clean it up and read the whole number. The number you are showing 2806830... means '68 to mid-'76 RG block (198/225), forged crank. You need to find out if it's a 225 or 198. The first number will tell you that.