On the "Ultimate" stick, the Suzo-Happ site shows
here that there is a different actuator for 8-way than 4-way.

To convert from 4-way to 8- way, remove actuator 95-1307-00 and flat washer 43-0057-00 -- replace them with actuator 95-0267-00. ($0.73 on the Happ site, you might want to PM Divemaster127 (you linked to his store in OP) to see if he has one for sale since he charges less than Happ for shipping.)
Protip: Find parts/details on Suzo-Happ site, but order them from Divemaster127.

Scott
EDIT: Just noticed that you also need to replace 95-0268-00 8-way bracket with 95-1314-00 4-way bracket. It is a non-stock item.
Adding the bracket swap changes the difficulty level from "clipping your fingernails" to "cutting out an ingrown nail" -- It's not major surgery, but it won't exactly be easy or painless, especially if you don't exactly know what you're doing.
If you ordered the stick from Divemaster127, you might want to ask him if he'll let you return/exchange it for a Happ Super

or Competition

, or an Ultimate 8-way if you have your heart set on that model.
