Dave:
You can swap the order of all the bits, 64 bits in the 8 bytes, by applying the byte swap algorithms that myself and others have suggested already. The you simply re-order the bytes.

In order to deal with a "shorter string" then take the resulting 8 byte string and implement a shift algorithm on it. You can shift it one bit at a time in XRAM by using DPTR to point at the string and loading each byte in turn into A. Multiple shifts would require a loop around the single bit/multi byte shift. As you are already into programming I'll leave it to you to work out the loops and such as opposed to writing the code for you.

Good Luck
Michael Karas