[Derek UK]

I'm not sure where the pin goes but it's used when swapping out the shells without dropping out the crank, engine still in car. You don't need to do that as you have the engine on the stand. What is stopping you just lifting the crank out? There is a possibility that you may have to get the mains journals ground. The shell wear is very bad compared to the big ends. Crank will need measuring. Being only a 3 bearing crank the shells take more of a beating than the 5 bearings in the B18/20. Does help them to rev though. Vaguely I seem to remember that I replaced the rear main bearing seal with the engine in the car, tapping the old top one out with the new.
Your shells will just tap out from the opposite side to the small locating tab/notch. Likely they will just pop out rather than slide round. To fit you squeeze them in with your thumb and they click into place.
By the time you read this they will likely be out anyway.
Pleased to be wrong about the rings. Depending on the measurements you might get away without a rebore etc, just new rings. An oil control set might, just might, be all you need. Second best to a rebore. Bores will need to be honed I expect. Ring gap is bad but recheck that the ring straight across the bore.