I called a local distributor to get a quote for replacement sticks, and best he could do was $175 per stick for Happ replacements. I didn't even want to guess what Sega would have changed for replacing these with original ones. Anyway, I found what looked like the exact same Happ sticks on ebay (marked new/overstock) for much cheaper (thank you ebay!) I got the new sticks in the mail, and they felt pretty stiff, this is actually a good sign, as I wanted accuracy, not loose analog sticks thats don't return to the center.
The mounting points on the plates were exactly the same, so no problem fitting them to the control panel. The only difficulty was in the proprietary Sega connectors. I rigged my own connectors and started up the machine, only to find they would not calibrate correctly. Apparently not all 5K pots are the same. So I then decided to pull out the original Sega pots, put them in the Happ sticks, using the original connectors, and low and behold it works!
Here are pics of the original stick, then the Happ ones I bought, and then what it looks like mounted in the control panel. I may try to attach the rubber boot to the Happ sticks, but it would require me to drill holes in the mounting plate...not sure if I feel like doing that at this point. I also have to tweak the center line of each pot to get the game to accurately perform the extreme left/right dodge maneuver, vital to playing the game accurately. I really can't imagine American arcade operators going to these lengths to make the game this playable...which also tells me why some people found the controls lacking.