Originally Posted by M5fly
How were you able to torque the nut reaming from the top down? I'd prefer that route but didn't think it was possible.
The plans for the 6 have you cut a hole in the firewall to get a socket on the nut. You then make a small cover and adhere it with proseal/RTV or pop rivet it on. As Don mentioned, you probably can make a depression deep enough to get a wrench on it. I used a metric M8 bolt to get a couple more thou and it made mine tight. Once the bolt is tight in it's bore, I don't believe you will have further wear. MIne is at 750 hours and still tight.
A 5/16 bolt (excluding close tolerance bolts) is usually a couple thou under .311. I believe the range is .307-.310. A metric bolt will be much closer to .311 (.310-.313), though there is a tolerance range so bring your calipar and pick through the bin to find the largest one. You want a fit just snug enough that light taps with a brass hammer are required to get it in. Be aware that the bore in the leg can be tight, but the bore in the sleeve still loose and that will require more work to get right. Both must be snug fits.
As mentioned, be sure the bolt has the FULL OD at the entry and exit point. Note that some bolts have a relatively long taper just before the threads. Just use extra washers. No issue busting the 3 washer rule here.