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The original stops were mounted on an aluminum plate with holes and springs. There was a problem with this since I planned on using SAMs for the stop actions. First the upper and lower rails were too thick and would cause the tabs to be recessed 3/8 of an inch too far, second the spacing of the holes in the aluminum frame spaced the tabs too far apart.
This necessitated removing some of the stock on the back of both rails. This was done with a rabbiting bit on the router, taking several passes to clean it up. This is shown in pictures 7 and 8.
Now we needed a backrail, something that the 321 did not have. Picture 9 shows the new backrail, exactly 2 inches higher than the original wood rail spacer that was in place. Picture 10 shows the backrail attached to the bolster for fitment before veneering and finishing.
Next, since the backrail was 2 inches higher the sides of the shell had to be raised the same amount. This is shown in picture 11. Since we are installing SAMs and they extend outward from the rail it was necessary to relieve the sides of the console inch as seen in picture 12. This left plenty of clearance for the SAMs. In the upper right corner of the picture you can see one of the pivot points used to hinge the bolster up and out of the way for service. Picture 13 shows one of the original face boards on the left and a new one 2 inches higher on the right. I was fortunate to have some finished scrap wood panels from another console that while not a great match they were acceptable to use rather than new wood that would have to be finished.
The keyboards were next. Pictures 14, 15 and 16 show this. They were cleaned, adjusted and then 18 pistons mounted in each of the 3 key slips. The current price of true thumb pistons is pretty steep and since most organists don't actually look at them when they press them I felt that another method was in order. These were momentary push buttons purchased from an eBay supplier in China. Cost was $37.00/100. Since the button in the center will rotate there was no point in engraving them. Picture 15 shows the slips as well as the back rail before veneering, 16 shows them installed and the keyboards in the shell.
The short bolsters were cut from 3 inch thick poplar stick 4 inches wide and then they were cut to width and veneered with the same veneer as the back rail. Pictures 17 and 18 show the short bolsters installed as  well as the back of the bolster and more detail of the hinge setup.