While it is possible that Reeves was natural (and he did have a look that was quite possibly, with gifted genetics, naturally achievable with many many years of hard work and intense dedication) I believe it was Kurt Marnul who said he was introduced to steroids by Reeves, as well as Reg Park discussing Reeves usage. I honestly find it very difficult to believe that this 'letter' is anything other than an Internet trolling.
Reeves was said to have been one of the pioneers introducing steroids to bodybuilding. Arnold (while certainly influential) freely admitted to the use of illicit substances to obtain his fantastic body. Only a stupid man would make such a plea, and Reeves certainly did not strike me as stupid.
It is phrased too well for a man who did not speak English as his first language. Add into it that he died over a decade ago, and I find it difficult to believe that this is anything more than someone who is disappointed with the mass monsters of today lashing out under a pseudonym.