Hi Jed (AD7KG).
I took a few more pictures of the hoist shelf today. As you can see, the back plate is about 18 & 1/2 in. by 18 & 1/2 in. overall. The shelf is 18 1/2" wide X 8 1/2" deep.
The two almost-square truss plates on the ends of the shelf are 7 1/2" wide X 7 1/4" tall but could easily be of any dimensions and triangular in shape.
All plate materials are 1/4" thick. If I were to do it over again, I would go with plate that's 3/8" thick. When raising and lowering the tower there's some bowing of the back plate in the direction of the tower. As you can see, there are three 1/4 X 1 3/4"" SS bolts at the top and three at the bottom securing the plate to the tower through the original horizontal mounting rails. When the tower moves up or down, there's a bit of a bow in the plate in the middle - especially when just starting or stopping the operation. If there had been a third horizontal mounting rail to attach the back plate to, there would be almost no plate deflection as there would be no unsupported mid plate to bow in the direction of the tower.
As to the cable... I removed the original cable from the spool and replaced it with the tower cable. If I recall, I removed four flush mounted bolts (can't see them now) from the bottom of the hoist's housing and slid the motor ass'y to one side, allowing me to deal with the spool and the cable attachment 'wedge'. It's a small pain in the ass, but nothing of any consequence. You'll see in the pictorial diagram that's included with the hoist that once the motor is free from its housing, the spool almost falls off, giving you easy access to the cable attachment point.
One other thing... in looking at the last photo in the group I noticed an unused bolt hole in the top and bottom horizontal mounting rails. I'm going to guess that those are originals along with the center ones. If I recall correctly, I drilled additional holes in both rails and then c-clamped the plate to them and marked through the holes with a pencil and then removed the plate to drill it. You'll notice that the bottom center bolt is turned in the opposite direction from the other five. When I mounted the hoist housing to the shelf, I wanted it sucked up against the back plate - as close as I could get it, to keep the cable's draw closer to it. I think what happened there was I ended up being short a bolt initially and mounted the hoist to the plate without it. Later when I went to add the missing bolt, I didn't have the room to insert it in the hole with the hoist housing in the way so I simply taped a washer and nut to a ruler and drove the bolt through the back of the plate to meet up with them, behind the the hoist. I chose bolts that were as short as possible to allow the tower to pass freely by the bolt ends. When it was all said and done - I could have easily turned all the bolts so that their heads were facing the tower as it passed instead of the other way around. Duh!
