I am not as well mannered as Al... Probably why he makes the big dollars... So I'll just answer in the best way I know how.

1) Your level III should have this worked out. Procedure development should have already covered the bases your requesting get covered here.
2) If you are the level III, you've already went off the rails. It's not possible to have made a calibration block without first having developed a valid scan plan for something like this. A valid scan plan will detail full coverage and how it is to be obtained. It will also detail sensitivity levels, the nature of reflectors required, angles, etc. You don't have a cal block, you have a boat anchor without having addressed the aforementioned information first.
3) You've mentioned Section VIII for joint design. We can only 'assume' your work is to be compliant to ASME Section VIII Div 1.
4) We have seen no drawing. I for one won't even attempt a guess without seeing it.
5) Even though I've developed corner joint UT procedures in various configurations, it wasn't run of the mill pipe or plate UT. It was a lot of painstaking work. Work I got, and usually get paid for. Even if I were so inclined to digress into altruistic help a brother out mode, it wouldn't help you. You could send all the great and wondermous details, a complete 'theoretical' model developed, ad nauseam, but without the expertise and vision on the ground to implement it, it would do more harm than good when the third party ANI, IACS, etc turned their experts on it. It won't take long for them to ferret out that it didn't come from you.

My advice is to stop while your ahead. Contract it out to someone who can do it (other than me).