If you can get the block or head casting number and you can tell what you have by going to this site and finding your number.
http://www.inliners.org/casting/numbers.html
on that page if you click CTRL + F (most web browsers) it will bring up a find window that you can type your number into and then click find.
What I have found a lot of times is the cast number to be worn down and or so grimy that you mistake a number for something else. best bet is to then find one that is close and then go back to the block or head and re-look at it to compare.
hope this helps.