The sha1 hash for 64test64xa is 6779c53432b8badf049bb9d8924a5785dd887243 which is 41 characters only using hexadecimal, 10digits and 6letters. But how long it would be if it was using the whole 26 letters in the latin alphabet? What if it also differentiated between UPPER and lower cases?
That would produce a binary stream. If that’s what OP wants, they could just leave the original hash in binary. And that would be unlikely to compress any further since hashes are, by their nature, high entropy already.