Cap'n
I'm no guru, but can maybe answer some of your questions. If you look on the Walbro site, it implys that two carburators were used on et EB431, ie WYK-67-1 & the one you have HDA 112-1 - both are cylinder type carbs but the WYK 67 doesn't have any needles - I can verify this as I had one of these carb's on the Redmax EB4401 I have converted. The closest I could come to EB431 on the redmax site is the EB4300. It has three bearings (two up front and one in the rear) and they look to be ball type. This is the same configuration as the EB4401. Hope this helps!
Sides7