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.
trillion -plus number and letter guessing to recover the op private key meaning nothing chance to get recover trillion alphanumeric private key is goes long time consume and possible to get negative result, i suggest to the op is better to move on than and forget it and start another investment and this a lesson always keep safe the private key to avoid lost funds.