Can you not use self tapping screws to fix the flange instead of nuts/bolts?
As for the ETB gauges, you can find a template for the speedo sensor that Pilgrim recommend to fix to the front of the diff
here. To get the gap to 2.5mm as recommended, use a small drill bit to measure. This should see that it works at all speeds.
As for bending back the fins, you do not need to. Call Pilgrim and they'll give you the calculation you need to program into the speedo. Did it for me and it needed no adjustment at all.
Cheers,
Tony B
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http://homepage.ntlworld.com/tony.breski