Zimmers has the 1581 Update-5 and -6 ROMs by TFSS with a little information but not complete. Specifically, Update-5 says:
Using 8K SRAM Expansion $2000-$3FFE, And MOSTECH 6529B PIO $3FFF for parallel data transfer routine from BARD'S TALE III.
The is pretty self-descriptive but is there an accompanying documentation showing how to perform the installations of the additional hardware? What about this parallel transfer routine in Bard's Tale III?
On a side note, Zimmers has what looks like the source code for the original 1581 ROM. I have mused upon the notion of an HD version or a dual-drive version of the 1581. Just because. Could be fun but not sure I want another "fun" project on my desk right now.