Considering the complexity of a wallet private key, the odds of guessing a 8-characters alphanumeric private keys are 1 in 2.1834E+14 (62^8). That's one in 218 trillion-plus. I don't think you have the chances of restoring those letters anymore.
Private keys aren't any random alphanumerics characters, they are usually encoded using some encoding scheme which means their set of characters are limited to a much smaller number.
In case of ethereum I believe it uses hexadecimal or base-16 encoding which means losing last 8 characters is equal to losing the last 4 bytes and the space to search is about 4.3 billion which is not that big a deal. But OP needs to have at least his address and preferably his public key to make this an easy possibility.