Hi Birdy,
Using Bullseye glass is a suggestion and its what the authors use for the shells. I have worked with 104 and BE too and while the 104's will work its just the BE is a little stiffer and can (for some) be better for sculpting. I made a shell yesterday and I saw the difference between BE and 104 coes..
I saw the sheet glass suggestion and again, there are some who use that with rods but I never have.
You can still use 104 glass with the tuts!