This image is the completed first step. Make note of the smaller end and the side the tail is sticking out of. The tail is used for pulling the small end through to the other side.
And the inverting process.
Before
After
Now, push the larger part back through, until the smaller end is flush with the webbing.
And here is the smaller end, flush with the webbing.
And as I had presumed would be possible, knitting this way will make this completely free to be used with any shell/body/etc pattern a person would want to use for their ammonite/cephalopod/squid/etc. I even held it up to a crocheted thing my wife made and to my knitted trilobites, and it works quite nicely. So, WEEEEEEEEEEEEEEEEEE!!! It’s good. Now I just have to actually write the patterns (Which will be quite a few as I’ll add 8 arm and 10 arm patterns for each, O_o).