"There are two drainage swales at 50 and 30 yards. I think the last two evergreens are just about at these distances. The recommendation was at 50. I think Wayne prefers 30."
In fact I prefer the placement in the earlier natural swale. The bunker at Merion's 5th is 32 or so yards short of the start of the green. If you look at the second to last photograph that is posted, the second tree shadow short of the green is where I would put a bunker within the fairway lines, just over 50 yards short of the green. That leaves plenty of room to fly the bunker and feed onto the green. Taking the safe route to the right of the bunker leaves a testing shot to the green falling away from you. Playing the second shot as a layup on the left side of the fairway leaves ground or aerial options.
"There is some concern about whether a ball will go over a proposed bunker and end up in the left bunker. There is also concern whether at 30 yards the downslope just after it would be too steep and close to the green to allow carrying it and staying on the green."
These are uniformed concerns. Who has these alledged concerns? The bunker I proposed was not 30 yards from the green.
"Because of the intricacies of the slope , I think building a good bunker is difficult."
Are you building the bunker? You really think that a good construction team could not build a good bunker there? You don't know what you're talking about; not that that ever stopped you before
By the way, how much experience do you have designing and building bunkers?
"The width. depth, length, relation to the center of the green all seem to point to the original design as the best alternative."
What does that mean? There is nothing of any substance in such a statement. Explain why. You make conclusive statements without any support at all and that contradicts expert restoration architects and just about everyone I've discussed this issue with.