Downloaded the disk image from:

https://archive.org/download/Uncracked4am

COMPUTIST No. 23 has a crack for this spreadsheet, but IMHO it can
be slighttly improved and furthermore it is missing the HD installation part.

From the original article we learn that there is a nibble check/count
routine "hidden" in block #7. The proposal patch is to change a 18 CLC with
a 38 SEC.

We noticed that you can completely bypass the check/count code replacing a 20 JSR
with a 60 RTS in block #7 byte 75.

Reboot and the program starts.

Now for the missing part:

1 - Start a disk with ProDOS and BASIC.SYSTEM on it
2 - insert the FlashCalc disk
3 - run INSTALL (a BIN file)
4 - set/change the prefix with one of your choice
5 - try 'I' and... we got an error!

A quick analisys of INSTALL reveals the presence of the same check/count
code contained in block #7.

So now we can follow the idea of the COMPUTIST article and replace in file
INSTALL at offset DB2 a 18 CLC with a 38 SEC.

We can do better: we are very lucky and we noticed that the carry flag is set
before the call of the check/count routine, so all we need is to replace
in file INSTALL at offeset 913 a 20 JSR with a 2C BIT.

Lets go to search all your VISICALC data files and convert them to ProDOS!